Category: Industry Trends

High Burden Tripping Types MVAJ 21. 23. 25. 26. and 29

These relays are suitable for use in high security circuit breaker tripping circuits.

particular they can be used in distributed tripping or control relay contact logic

where the initiating contact may be remote from the relay. The relays have a high

which is either cut-off at operation or economized to a low figure, either

or after a time delay.

The high burden provides immunity to capacitance discharge currents, which can result

the inception of an earth fault on battery wiring and immunity to the subsequent

current.

The high burden also permits the use of supervision relays such as type MVAX where

wiring is at risk and provides reliable operation of series elements such as repeat

type MCAA. For the latter purpose, type MVAJ relays can be provided with a time

economizing feature.

Control Relay Type MVAJ 34

This is a dual-rated electrical-reset relay, the main function of

which is to switch protection and autoreclosing equipment in and

out of service from a remote point via pilot wires. It complies with

NGC SPEC. NGTS2.19:1996.

The MVAJ 11 to 34 range complements the more cost-effective range of MVAJ 051 to

MVAJ 205 tripping relays catering for the preferences of historical users.

MVAJ general characteristics can be found in table 1 that includes information on how

relay burden is modified at, or just after operation. ‘Economy’ indicates that the burden

reduced to a low value.

Instantaneous cut-off is a feature of some hand and electrical-reset elements and

the burden to zero, whilst others incorporate a time delay to enable series elements

operate. This time delay is 40 ms to 60 ms in all cases, except that of  type MVAJ 26

the delay is 2 s. All low burden relays are suitable for AC or DC operation. All high

relays are for DC operation only.

Types MVAJ 23. 25 High Burden Tripping Relays

with Instantaneous Cut-off

These relays incorporate a break contact in series with the

operate coil. Located on the main contact stack, it is arranged to

break the coil circuit once the relay mechanism has completely

operated. This reduces the relay burden to zero as soon as

mechanical latching of the contacts has occurred.

MVAJ 10. MVAJ 20

When configured for high burden applications, the burden is

either cut off or is economised to a low figure after a 40-60 ms

time delay. Due to the greater minimum operating current, the

high burden application also permits the use of supervision relays

such as type MVAX 11. where the wiring is at risk. The 40- 60 ms

time delay ensures reliable operation of series elements such as

type MCAA repeat relays.

Type MVAJ 102 relay is specifically designed for applications

requiring a tripping relay which is self-resetting after a nominal

delay of 2.5 seconds. This relay may be used, for example, for

inter-tripping between higher voltage and low voltage circuit

breakers of a large 3-phase power transformer.

This may become necessary when the high voltage circuit

breaker is tripped after a heavy internal fault by protection

which cannot conveniently provide an auxiliary contact with a

dwell time long enough to ensure correct tripping of the low

voltage circuit-breaker.

Typically, the relay is initiated by transformer protection, such as

overall protection, restricted earth fault and Bucholz relays, in

arrangements where both the HV and LV circuit-breakers are to

be tripped simultaneously.

The HV breaker may be expected to trip more quickly than the LV

breaker so the tripping signal is maintained by the delayed reset.

This ensures complete clearance by the LV circuit-breaker, even

though the fault may have been cleared largely by the HV breaker

and the protection has started to reset.

High Burden Application

These relays, supplied as high burden, are suitable for use in high

security circuit-breaker tripping circuits. The high burden provides

greater immunity to capacitance discharge currents, which can

result at the inception of an earth fault on battery wiring. This

makes the relays particularly suitable for use in distributed

tripping or control relay contact logic schemes, where the

initiating contact may be remote from the relay.

MVAJ 05

When configured for high burden applications, the burden is

either cut off at operation or is economised to a low figure

instantaneously.

Low Burden Application

These relays are suitable for general applications where the

initiating contact is located close to the relay. When configured

for low burden applications, by removing the external link from

terminals 22 and 24. the burden is either cut off during operation

or is economised to a low figure instantaneously.

Models Available

• Trip relays

Trip relays possess a standard hand-reset flag and operate within 10 ms.

Table 1 shows  the trip relay versions available

• Control relays

Control relay variants of each trip relay are available. These relays operate within

approximately 15 ms

All relays configured for high burden applications are suitable for DC operation only

Applications

Self-reset relays reset when the initiating signal is removed,

making them suitable for use as trip relays in auto-reclose

schemes and also for general flagging purposes. Hand-reset relays

require manual resetting, making them effective lockout relays

which are commonly used to trip circuit-breakers associated with

transformers. Electrical-reset relays require a voltage to be

applied to the unit to reset the contacts. These relays may be

used in auto-reclose schemes, or where remote resetting of the

relay is required.

Trip Relay

With the exception of the MVAJ 102 time delayed self-reset

relays, all trip relays are suitable for either low burden or high

burden applications.

Protective relays are precise measuring devices, the contacts of which

should not be expected to switch large electrical loads.

In some cases, the protective relay can trip a circuit- breaker directly,

or according to coil rating and the number of circuits to be energised.

The MVAJ relay interfaces with the protection to provide: higher contact

additional contacts for tripping multiple circuit-breakers, control functions,

signalling interlocking.

The MVAJ range comprises very reliable hinged armature relays designed

to operate circuit-breaker trip coils. Built to very high specifications, the

MVAJ range a highly flexible and reliable link between the protective relays

and the circuit-breakers.

Low Burden Application

These relays are suitable for general applications where the

initiating contact is located close to the relay. When configured

for low burden applications, by removing the external link from

terminals 22 and 24. the burden is either cut off during operation

or is economised to a low figure instantaneously.