Description

Low Burden Tripping Relay Types MVAJ 11. 13. 14

These relays are suitable for applications where immunity to

capacitance discharge and high minimum operation currents are

not required.

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.

High Burden Tripping Relay Types MVAJ 21. 23. 25. 26. 27

Versions have one or two contact stacks depending on the number

of output contacts required.

Type MVAJ 21 High Burden Self-resetting Relay

This uses a contact on the main contact stack to energize a

separate, rear-mounted economizing element. After operation,

this reduces the burden by switching in resistance in series with

the main element and switching out shunt resistance.

Figure 2 shows a typical circuit diagram for self-resetting relays of

this type with high speed economy. When the main attracted

armature unit RL1 is energized by the protection contact PR, a

contact RL1-a energizes auxiliary element RL2. When contacts

RL2-a and RL2-b open, resistor R4 is put in series with RL1 while

the circuit to resistor R2 is broken.

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.