Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions
Microprocessor-based protection relays are gradually driving out traditional electromechanical and even electronic protection devices from virtually all fields of power and electrical engineering. In this paper, one of many problems of microprocessor-based relays is discussed: nonconformance of mini...
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Інститут технічних проблем магнетизму НАН України
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| Цитувати: | Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions / V. Gurevich // Електротехніка і електромеханіка. — 2006. — № 1. — С. 12-16. — Бібліогр.: 9 назв. — англ. |
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irk-123456789-1426272018-10-14T01:23:07Z Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions Gurevich, V. Електричні машини та апарати Microprocessor-based protection relays are gradually driving out traditional electromechanical and even electronic protection devices from virtually all fields of power and electrical engineering. In this paper, one of many problems of microprocessor-based relays is discussed: nonconformance of miniature electromechanical output relays under actual operation conditions: switching inductive loads (with tripping CB coils or lockout relay coils) at 220 VDC, and "dry" switching of some control circuits. We suggest a simple and very reliable solution to this problem: an electronic amplifier for increase in switching ability of the output relays. Мікропроцесорні реле захисту швидко витісняють традиційні електромеханічні і навіть електронні пристрої захисту практично у всіх областях електроенергетики. У статті розглядається одна з численних проблем мікропроцесорних реле: невідповідність параметрів вихідних елементів цих реле, виконаних на основі мініатюрних електромеханічних реле, реальним умовам експлуатації: комутації індуктивного навантаження (котушок вимикачів) при напрузі постійного струму 220 В і так звана "суха" комутація кіл управління. Запропоновано простий і надійний підсилювач спеціальної конструкції для збільшення комутаційної спроможності вихідних реле. Микропроцессорные реле защиты быстро вытесняют традиционные электромеханические и даже электронные устройства защиты практически во всех областях электроэнергетики. В статье рассматривается одна из многочисленных проблем микропроцессорных реле: несоответствие параметров выходных элементов этих реле, выполненных на основе миниатюрных электромеханических реле, реальным условиям эксплуатации: коммутации индуктивной нагрузки (катушек выключателей) при напряжении постоянного тока 220 В и так называемая "сухая" коммутация цепей управления. Предложен простой и надежный усилитель специальной конструкции для увеличения коммутационной способности выходных реле. 2006 Article Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions / V. Gurevich // Електротехніка і електромеханіка. — 2006. — № 1. — С. 12-16. — Бібліогр.: 9 назв. — англ. 2074-272X http://dspace.nbuv.gov.ua/handle/123456789/142627 621.316+004.315 en Електротехніка і електромеханіка Інститут технічних проблем магнетизму НАН України |
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Електричні машини та апарати Електричні машини та апарати |
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Електричні машини та апарати Електричні машини та апарати Gurevich, V. Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions Електротехніка і електромеханіка |
| description |
Microprocessor-based protection relays are gradually driving out traditional electromechanical and even electronic protection devices from virtually all fields of power and electrical engineering. In this paper, one of many problems of microprocessor-based relays is discussed: nonconformance of miniature electromechanical output relays under actual operation conditions: switching inductive loads (with tripping CB coils or lockout relay coils) at 220 VDC, and "dry" switching of some control circuits. We suggest a simple and very reliable solution to this problem: an electronic amplifier for increase in switching ability of the output relays. |
| format |
Article |
| author |
Gurevich, V. |
| author_facet |
Gurevich, V. |
| author_sort |
Gurevich, V. |
| title |
Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions |
| title_short |
Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions |
| title_full |
Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions |
| title_fullStr |
Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions |
| title_full_unstemmed |
Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions |
| title_sort |
nonconformance in electromechanical output relays of microprocessor-based protection devices under actual operating conditions |
| publisher |
Інститут технічних проблем магнетизму НАН України |
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2006 |
| topic_facet |
Електричні машини та апарати |
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http://dspace.nbuv.gov.ua/handle/123456789/142627 |
| citation_txt |
Nonconformance in Electromechanical Output Relays of Microprocessor-Based Protection Devices under Actual Operating Conditions / V. Gurevich // Електротехніка і електромеханіка. — 2006. — № 1. — С. 12-16. — Бібліогр.: 9 назв. — англ. |
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Електротехніка і електромеханіка |
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AT gurevichv nonconformanceinelectromechanicaloutputrelaysofmicroprocessorbasedprotectiondevicesunderactualoperatingconditions |
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2025-07-10T15:25:06Z |
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2025-07-10T15:25:06Z |
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Електричні машини та апарати
12 Електротехніка і Електромеханіка. 2006. №1
УДК 621.316+004.315
NONCONFORMANCE IN ELECTROMECHANICAL OUTPUT RELAYS OF
MICROPROCESSOR-BASED PROTECTION DEVICES UNDER ACTUAL
OPERATING CONDITIONS
Gurevich Vladimir, Ph.D
Israel Electric Corp., Central Electric Laboratory
POB10, Haifa 31000, Israel
Fax: (++1) 603-308-5909, E-mail: gurevich2@bezeqint.net
Мікропроцесорні реле захисту швидко витісняють традиційні електромеханічні і навіть електронні пристрої захис-
ту практично у всіх областях електроенергетики. У статті розглядається одна з численних проблем мікропроцесор-
них реле: невідповідність параметрів вихідних елементів цих реле, виконаних на основі мініатюрних електромеханіч-
них реле, реальним умовам експлуатації: комутації індуктивного навантаження (котушок вимикачів) при напрузі
постійного струму 220 В і так звана "суха" комутація кіл управління. Запропоновано простий і надійний підсилювач
спеціальної конструкції для збільшення комутаційної спроможності вихідних реле.
Микропроцессорные реле защиты быстро вытесняют традиционные электромеханические и даже электронные
устройства защиты практически во всех областях электроэнергетики. В статье рассматривается одна из много-
численных проблем микропроцессорных реле: несоответствие параметров выходных элементов этих реле, выполнен-
ных на основе миниатюрных электромеханических реле, реальным условиям эксплуатации: коммутации индуктив-
ной нагрузки (катушек выключателей) при напряжении постоянного тока 220 В и так называемая "сухая" коммута-
ция цепей управления. Предложен простой и надежный усилитель специальной конструкции для увеличения комму-
тационной способности выходных реле.
Microprocessor-based relay protection devices are
gradually driving out traditional electromechanical and
even electronic relay protection devices from virtually all
fields of power and electrical engineering. Whether this is
good or bad may be open to debate (the advantages of
microprocessor-based protection means over the tradi-
tional are far from being absolute or obvious) yet we must
acknowledge that this is the general trend. While ac-
knowledging this trend we must also note that microproc-
essor-based protection means do have several specific
drawbacks. In this paper one of these problems will be
discussed.
1. Microprocessor-based relay protection devices
(hereinafter MRPD) with different functionalities (differ-
ential, distance protection, generators protection, capaci-
tor banks protection, etc.), made by different leading
companies in the world such as ABB, General Electric,
Areva, Alstom, Cooper, and Crompton Instruments, were
analyzed for compliance of output of the electromagnetic
relays used in these MRPD, with the standard require-
ments and parameters set forth in the manufacturers’
specifications and the actual operating conditions in the
power systems.
2. It was established that in all types of MRPD elec-
tromagnetic relays of the same class were used as output
elements: subminiature relays with one make or change-
over contact enclosed in a sealed plastic box having di-
mensions of about 30 x 10 x 12 mm (Fig. 1). These are
G2RL, RY6100 G6RN, RTE24012, ST2, JS and similar
relays made by the Schrack, Omron, Matshshita, and Fu-
jitsu companies. Normally the maximal values of
switched voltage and switched current are marked on the
bodies of the subminiature relays, in contrast to the
maximal switching power and the type of current to
which these current values are related, which are usually
omitted. This creates a problem when choosing the relay
since maximal switched power is not equal to the multiple
of maximal switched voltage and maximal switched cur-
rent. For adequate evaluation of the switching ability of
such relays the accompanying technical documentation
needs to be analyzed.
Fig. 1. PCB boards of MRPD with output electromechanical
relays of different types
The results of our analysis of technical documenta-
tion accompanying these subminiature electromagnetic
relays are presented in Table 1.
As can be seen from the table, all of the relays have lim-
ited DC switching ability and are only suitable for switch-
ing of merely active loads.
Електротехніка і Електромеханіка. 2006. №1 13
Table 1
Switching capability of subminiature electromechanical relays using in MRPD
Maximal Switching Power
(for resistive load)
Rated Current & Voltage
(for resistive load) Relay Type (Manufacturer)
AC DC AC DC for 250 V DC
ST series (Matsusita) 2000 VA 150 W 8 A; 380 V 5 A; 30 V 0.40 A
JS series (Fujitsu) 2000 VA 192 W 8 A; 250 V 8 A; 24 V 0.35 A
RT2 (Schrack) 2000 VA 240 W 8A; 250 V 8A; 30 V 0.25 A
RYII (Schrack) 2000 VA 224 W 8A; 240 V 8A; 28 V 0.28 A
G6RN (Omron) 2000 VA 150 W 8 A; 250 V 5 A; 30 V -
G2RL-1E (Omron) 3000 VA 288 W 12 A; 250 V 12 A; 24 V 0.30 A
This can be attributed to very hard DC operation
conditions of relay contacts with inductive loads, result-
ing in considerable overloads that are likely to cause a
breakdown of the very small dielectric gap between the
relay contacts which maintains arching on the contacts, as
well as nonoccurrence of periodic current zero crossing,
characteristic of AC. Voltage across the contacts may
become six-fold the value of the nominal voltage. When
the voltage over the contacts exceeds 50 V a strong spark
is generated at switching such a load that causes strong
erosion of the contacts. As the applied voltage is in-
creased (to 100-150 V), the spark at the relay contacts is
changed to a stable arc, which totally melts even powerful
contacts (rated for nominal currents of 10-15 A) within
0.5-1.0 seconds at a current of 0.5-2 A. Therefore the
switching ability of DC relays is much lower than that of
AC relays (Fig. 2), however, according to the manufac-
turers of MRPD, subminiature relays installed in MRPD
are designed for the direct making of tripping coils in
high voltage circuit breakers - CB (for line protection) or
for the making of lockout relays – powerful intermediate
latching relays with a manual reset (for transformer pro-
tection), namely for engaging inductive loads in 220 V
DC circuits – the heaviest duty for relays. What are these
loads under actual operating conditions?
Fig. 2. Typical relations between commutation parameters (volt-
age, current) and load characters for relay contacts
Table 2 includes the results of analysis of tripping
coil parameters for different types of circuit breakers
made in different countries.
As can be concluded from the comparison of the
abovementioned relay parameters (Table 1) and the pa-
rameters of the tripping coils of CBs (Table 2), the
switching ability of subminiature relays for DC circuits
(0.3 – 0.4 A) not at all sufficient for the direct making of
tripping coils of CBs (the required currents are 1- 6 A).
Connecting of lockout relays between output MRPD re-
lays and high voltage CB still does not provide a solution
since the self-current consumed by the coil of lockout
relay (2 A for the HEA type relay and 2.8 A for a modern
HEA63 relay made by General Electric) falls into the
same range of currents of tripping coils of CBs.
The situation becomes even more complicated be-
cause switching of the DC inductive load for these relays
cannot be foreseen at all, so subsequently the use of these
relays for direct switching of tripping coils of CB’s, as
well as intermediate lockout relays, results in the genera-
tion of loads beyond those allowed.
3. What do the standards and technical documenta-
tion related to MRPD say?
According to the ANSI/IEEE C37-90-1989 and
IEEE Standard for Relays and Relay Systems Associated
with Electric Power Apparatus [1]. Part 6/7: Make and
Carry Ratings for Tripping Output Circuits establishes
that the making current and the carry current accompany-
ing it for 4 seconds that is provided by the contacts of the
input relays controlling the tripping coil of CBs shall at
least 30 A. Why is this current value so high in compari-
son with the actual currents in disconnecting switches?
Because the AC tripping coil (a solenoid with a movable
core) has considerable starting currents (up to 10-fold)
caused by a low initial impedance of a solenoid with an
extended core. For devices with alternating operation cur-
rent such requirements are quite justified.
It is reasonable that in the view of this requirement
MRPD manufacturers included this parameter in the stan-
dard provided by their MRPD devices. In this way the
MRPD specification with regard to this parameter totally
complies with the standard requirements. However the
situation is different for the MRPD themselves, since the
specifications for specific types of output electromagnetic
relays do not mention at all the capability to switch 30 A
of current, even if it is AC.
Here we should be more precise and mention that
specifications for some types of special extended power
subminiature relays (not used in MRPD) mention the in-
rush current, i.e. short duration making currents reaching
values of up to 30 A. These relays are as if specifically
designated for use in MRPD. Maybe if MRPD manufac-
turers were requested to use these relays this would pro-
vide a solution to the problem?
The issue turns out to be not so simple, as there are
some other standards related to the relay switching modes
[2, 3, 4, 5]. In particular the IEC 60947-4 [4] standard, in
which the switching modes of relays and contactors are
divided into so called “categories of application”, speci-
fies requirements for contact relays operating in these
modes. In particular the contacts designated for control-
ling the electrical magnets of other intermediate relays,
contractors, solenoids and valves are classified as AC-15
for AC and DC-13 for DC (Table 3).
14 Електротехніка і Електромеханіка. 2006. №1
From the Table 3 it follows that increased (ten-fold)
switching current of the relay at closing (making capac-
ity) with respect to nominal current, is allowed only for
AC. In switching of DC circuits this increase does not
exceed 10%. This is accounted for by fact that not all
making of relay contacts is terminated after the initial
contacting of those contacts. Actually the making process
is always accompanied by the contacts bouncing after
their first closing. Relay contacts make several open-close
cycles of contact bounce before coming to rest in the final
state, Fig. 3 [6].
Table 2
Parameters of tripping coils of high-voltage circuit breakers
Trip Coil Circuit Breaker Model Circuit Breaker Kind Rated Voltage, V DC Rated Current, A
ELK SD14 (ABB) SF6 , 170 kV, 4000 A 220 2.3
B3-S101 (ALSTOM) SF6 , 170 kV, 2000 A 220 0.7
CPRG180/10-360 (AEG) Generator CB for 13.8 kV 110 2.0
3AP1F1 (Siemens) Oil CB, 245 kV, 3150 A 220 5.8
BBP-6-10/630 (Russia) Vacuum CB, 10 kV, 630 A 100 5.0
ВБГ-35 (Russia) SF6 , 35 kV 220 2.5
BBOA-15-14/12500 (Russia) Air CB, 15 kV, 12500 A 220 4.5
Table 3
Switching capacity of contacts depending on the type of load for control electromagnets, valves and solenoid actuators
Switching capacity of contacts
in the mode of normal switching
Make (switching ON) Break (switching OFF)
Utilization
Category
IEC 60947-4
Type of
current
current voltage cosϕ current voltage cosϕ
AC-15 AC 10 IN UN 0.3 10 IN UN 0.3
DC-13 DC IN UN - IN UN -
Switching capacity of contacts in the mode of infrequent switching
AC-15 AC 10 IN 1.1 UN 0.3 10 IN 1.1 UN 0.3
DC-13 DC 1.1 IN 1.1 UN - 1.1 IN 1.1 UN -
IN and UN are rated values of currents and voltages of electric loads switched by relay contacts
Fig.3. Oscillogram of relay making process with real measured
relay contact bounce
This contact-bounce interval is in addition to the re-
lay's operate and release times, which can measure (upon
the type of relay) from ones millisecond for small relays to
tens of milliseconds for lager relays. Therefore, all other
factors being the same, the making power of the contacts of
a DC load relay is much lower than that of an AC one.
From the above it follows that short duration making
currents of 30 A (3.75 IN) for subminiature relays may be
allowed only in AC circuits (even though this restriction for
the use of relays is not pointed out in any of the specifica-
tions, for obvious reasons!). That is quite reasonable since
there is no DC making currents at solenoid and control coil
activation. From here it also follows that when the tripping
coil of the CB is controlled by DC 220-250 V circuits, the
allowed value of making current for contacts is only 110%
of the nominal value, namely within a range of 0.35 –
0.45A, which is much lower that the actual currents.
In actual operating conditions output relays of
MRPD are operated relatively rarely (only in case of fail-
ures in the networks), which postpones detection of
switching problems. This saves MRPD manufacturers
from customers’ claims. Because of erosion that is inten-
sified at each relay operation the contacts surface condi-
tion is gradually deteriorated and their resistance and
heating increased, which results in welding of the contacts
during the next switching. In the course of the above re-
search we have approached many manufacturers of sub-
miniature relays with a request for an opportunity to use
their relays for making without breaking currents of in-
ductive load at a voltage 220 V DC and we received the
following answers:
a) The danger of welding of contacts may be very
great because of bouncing;
b) The relay to be used only in the authorized modes
specified in the technical specifications.
Moreover, in some cases, for example for acceler-
ated (forcing) operating of the CB (used in some types of
Siemens CBs, for example) a special circuit is used
(Fig. 4) that provides higher making current of up to
75 A. Direct connection of contacts of subminiature re-
lays in such circuits is prohibited.
Fig. 4. A circuit diagram for forcing switching of the CB trip-
ping coil (L)
Електротехніка і Електромеханіка. 2006. №1 15
4. There is an additional problem: the electrical
strength of the insulation of the inter-contact gap of the
output relays [7, 8]. Standard IEC 60255-5 [8] does not
define the test voltage that must be withstood by the open
contacts of output relays and suggests that the MRPD
manufacturer and the consumer agree on it, in accordance
with the specific operating environment. Such an ap-
proach is reasonable since only in some cases are the con-
tacts of output MRPD designated to switch inductive
loads under a constant voltage of 220-250 V. However, a
circuit that includes the contacts of an input relay is a
powerful DC network of substations. Powerful electrical
devices connected in the circuit (intermediate relays, con-
tactors, solenoids) have high-inductance control windings,
whose switching results in generation of significant over-
voltages. Therefore a question arises; to which type of
switching devices should the output MRPD be attributed?
Their requirements will be determined accordingly. On
the one hand, they are the internal elements of measure-
ment relay (MRPD is a measurement relay), to which the
IEC 60255-5 standard applies. On the other hand, they
can be easily attributed to electromechanical relays and
contactors. There is a separate standard for each type of
switching device (see list of references). Some of these
standards include a great number of requirements; from
the design parameters of the electric strength of the relay
insulation, to the point of the gap between the contacts,
and the distance between the outlets of the relay mounted
on the printed board. In order to make things easier, some
standards and instruction manuals for relays offer a sim-
plified formula for defining the minimal needed values of
the test voltage for industrial relays maintained for 1 min-
ute: U = 2UN + 1000 (but not less than 1500 V for appara-
tus with nominal voltage above 60 V). For a voltage of
250 V this yields a value of 1500 V. The analysis of tech-
nical parameters of a great number of industrial relays
shows that for this class of relays the maintained test volt-
age is within the range of 1500 – 2500 V, whereas in the
subminiature relays used on MRPD these values do not
go beyond 1000 V, in other words they do meet even the
lowest level of requirements for the strength of inter-
contact gap of industrial relays. The problem is not only
in the contact gap, but also due to the insufficient distance
between the pins of the subminiature relays. Under real
conditions of operation (moisture, dust) there is a high
probability of breakdown for some types of subminiature
relays between the pins on the surface of the PCB board.
Therefore manufacturers of MRPD sometimes make spe-
cial rabbets on a PCB board between the relay pins in
order to prevent such breakdowns. Unfortunately, some-
times not only the subminiature relays, but also other
components of the MRPD, chosen for reason of minia-
turization rather than reliability, are also involved. Fig. 5.
Fig. 5. Fragment of PCB board of MRPD with rabbets:
1 – between pins of main connector;
2 – between pins of output relays
5. Not all contacts of output relays are designated for
switching high power loads. Some of them are used as so
called “dry” contacts in electronic control circuits of other
microprocessor protection devices, local controller or data
transmission devices. A circuit or a contact is called “dry”
when the currents switched by it are so small that the con-
tacts are completely free of sparks at switching. This also
turns out to be faulty terminology since in the absence of a
spark the oxide films on the coating are not destroyed,
which results in significant deterioration of the contact
quality. When the coating thickness is too large the contact
resistance is so increased that “dry” circuit switching be-
comes virtually impossible [9]. This is particularly relevant
for miniature relays with low contact pressure and small
contact shift, and that is the reason for limiting the lower
boundary of switched current or power. This value may be
different for different types of contact coatings. For exam-
ple, in the mentioned ST2 type relay the minimal allowed
value of current is 100mA. Obviously, this relay cannot be
used for reliable switching of a “dry” circuit. When order-
ing MRPD, the minimal switched current and voltage
should be included as the most important values in the
technical specifications, and compliance should be in-
spected and verified by opening of the MRPD.
6. With regards to the problem of correctness of the
technical parameters represented in the MRPD specifica-
tions, it should be mentioned first of all that the values for
specific parameters of a particular MRPD are often pro-
vided in different documents that are essentially distinct,
and secondly that in some cases such incorrectness verges
on absurdity. For example, one of the specifications for
MRPD drawn up by one of the major companies (“Output
relays” section) says:
Making capacity: 1000 W (VA) at L/R = 40 ms
This entry has several major mistakes:
a. Making capacity does not provide information
about restrictions in relay use because of undefined cur-
rent and voltage.
b. Switching ability of the DC and AC relay contacts
for active load is different by about an order of magnitude
(see above), therefore the value 1000W(VA), stipulating
for equal power values for both DC and AC, is incorrect.
c. The inductivity of the load in the form of an L/R
ratio is given only for DC. For AC the inductivity of the
load is expressed in terms of the power factor (PF) or cosϕ.
d. Assuming that the term “Making capacity” means
“Switching capacity” the value 1000 does not match the
actual parameters of any relay used in MRPD. For AC it
is a twofold underestimation (exactly), whereas for DC it
is a 5-fold overestimation.
e. As mentioned above, switching of the inductive
DC load is not stipulated for the mentioned subminiature
relays, and is not mentioned at all in the specifications.
The specifications for another microprocessor relay
made by the same company read:
Brake capacity DC: 50W (resistive),
62.5 W (inductive L/R=50 ms)
This entry is unreasonable, since the allowed break
capacity of the inductive DС load, being higher than that
of the active load, contradicts all postulates of electrical
engineering. Moreover, the same specifications say:
Make & Carry: 30 A for 3sec;
Carry: 250 A for 30 ms
We could not find any mention of 30A, and all the
more of any 250A currents, in any of the specifications
for the mentioned types of subminiature relays.
These are only a few examples of incorrect informa-
tion included in such important documents as technical
specifications.
16 Електротехніка і Електромеханіка. 2006. №1
7. The problem becomes even more complicated
since at infrequent protection operation the mentioned
discrepancies in MRPD are not detected at once. Under
these conditions MRPD can function well for a couple of
years, during which the output relay contacts accumulate
defects that eventually lead to a sudden failure, resulting
in serious damage. Provided the device can operate for
several years without visible faults, it is difficult to pre-
sent a claim to the manufacturers of MRPD. It is also
quite difficult to determine the exact working life of a
relay operating under such conditions, and to predict
when damage is due.
8. What can be done in this situation? The MRPD
manufacturer should be requested to install several output
relays, complying completely with the standard require-
ments for industrial relays. It should be noted that in the
past this approach was very popular in semiconductor
protection devices (Fig. 6), however at present it is not
practicable, as this would require a major change in the
MRPD structure, and an increase in size.
Fig. 6. A static (electronic) protection device with large-output
electromechanical relays of industrial type, placed in separate
cell (OR – output relays)
The problem could be resolved by having the user
connect external power amplifiers between the MRPD
output relay and the tripping coil of the CB. This ampli-
fier would have to be simple, fast-acting, jam-resistant
and highly reliable under actual operation conditions.
9. We have analyzed the technical parameters of
various strong-current solid-state relays (SSR) made by
the leading companies in the world (ABB, Tyco Electron-
ics, Crouzet, Teledyne, Magnecraft, Celduc, Crydom,
Comus, etc.) and determined that each production sample
SSR has at least one or more parameters that do not com-
ply with the requirements essential for their use as a
power amplifier of output MRPD relays. Such parameters
as maximal DC voltage withstood over the main elec-
trodes in a cut-off state, which must be at least 1500 V;
making current in DC circuits with an inductive load,
which must be at least 5 - 10 A; operational suitability in
DC circuits (many SSR can be operated only in AC cir-
cuits); and make-time which must be not more than 1ms.
10. Due to unavailability, in today’s market, of
power amplifiers confirming to the requirements of com-
bined operation with MRPD, we have developed an am-
plifier conforming to these requirements. Due to its sim-
ple structure (Fig. 7), in-house making of this amplifier by
the electric power companies is quite possible.
The main switching element of the device is a par-
ticularly small-sized thyristor VT designed for current up
to 30A and voltage up to 1600 V. It has additional protec-
tion against spikes by means of an varistor RV with
clamping voltage of 1200 V (at nominal mains voltage of
250 V this provides high reliability of the varistor). With
the help of a special normally closed high voltage optical
coupler Opt the thyristor is forcedly blocked in the OFF-
state in order to prevent its accidental switching by in-
duced voltage or noise signal. The thyristor is switched
ON by the control current flowing in the thyristor control
circuit at closure of contact K of the output relay MRPD.
Capacitor C (0.01 µF 1600 V) is used as an additional
filter preventing the noises reach the thyristor. Unfortu-
nately only a few of the thousands of electronic compo-
nents available in the market comply entirely with the
requirements. In the first place this relates to the thyristor
VT (type 30TPS16, STMicroelectronics) and optical cou-
pler Opt (type TLP4597G, Toshiba). In order to provide
higher reliability and faster response of the device it is
recommended to use only these elements.
Fig. 7. Switching amplifier for output MRPD relays:
K – contact of output MRPD relay ; L – tripping coil of CB
11. In order to enhance the general reliability level
of the operation of electronic equipment having electrical
contact with DC 250 V mains, it is advisable to install
special protective devices for protection of sensitive elec-
tronic equipment (the mentioned MRPD, for example)
from spikes, generated at switching of inductive loads
(intermediate relay windings and contactors, solenoids of
actuator component drives, etc.) at the electronic equip-
ment termination point. Protective device of Limitor-VTS
type (ABB Stotz-Kontakt GmbH) includes a powerful
varistor and a fuse disconnecting the varistor from the
mains in case it is damaged (and also generating a visual
or distant failure alarm signal) is a good solution.
REFERENCES
[1] IEEE C37.90-1989. Relays and Relay Systems Associated
with Electric Power Apparatus.
[2] IEC 60947-4-1. Low-voltage Switchgear and Control Gear
– Part 4: Contactors and Motor- Starters – Section1: Elec-
tromechanical Contactors and Motor-Starters.
[3] IEC 60947-5-1. Low-voltage Switchgear and Control Gear.
Part 5: Control Circuit Devices and Switching Elements.
Section 1: Electromechanical Control Circuit Devices.
[4] IEC 60947-6-2. Low-voltage Switchgear and Con-
trol Gear – Part 6: Control and Protective Switching
Devices.
[5] IEC 61810-1. Electromechanical Non-Specified
Time All Or Nothing Relays - Part1: General Re-
quirements.
[6] Leyva P. Interfacing switches and relays to the real world
in real time. EDN Magazine, June 5, 2001.
[7] IEC 60664. Insulation Coordination Within Low Voltage
Systems, including Clearances and Creepage Distance for
Equipment.
[8] IEC 60255-5. Electrical Relays – Part 5: Insulation Coordi-
nation for Measuring Relays and Protection Equipment.
Requirements and Tests.
[9] Brun H., Johler W. Reliable Switching of Minimum Loads.
53rd International Relay & Switch Technology Conference.
IRSTC, April 18-20, 2005, California
Надійшла 01.07.2005
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