Archives

Application

High burden tripping relays: Types MVAJM 15. 25. 41. 45

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

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

schemes where the initiating contact may be remote from the relay.The high burden

provides immunity to capacitance discharge currents, which can result at the inception

of an earth fault on battery wiring and immunity to the subsequent leakage current.

The high burden relays are recommended for use with series connected operation

indicators, supervision relays and series seal-in units on protective relays.

Low burden tripping relays: Types MVAJM 11. 13

These relays are suitable for applications where immunity to capacitance discharge and

high minimum operation current are not required. These relays are generally used

when a number of simultaneous operations are to be initiated by a single protective

relay having insufficient contacts of its own and where series connected operation

indicators are not used.

Control relay: Type MVAJM 14

This is an electrically reset control relay. The relay is meant for switching the secondary

circuits of current transformer in busbar protection. Also wherever “latch-in” type of

control relay is required for contact multiplication control schemes, relay type MVAJM

14 can be employed.

Models available

Type MVAJM relays may broadly be divided into three groups:

! High burden tripping relays

! Low burden tripping relays

! Control relays

Features

! High speed operation

! High degree of mechanical stability

! Positive action without chatter

! Proof against high capacitance discharge currents

Customer Benefits

! Directly operates circuit breaker trip coils

! High reliability

! High speed operation

! Immunity to wiring capacitance discharge

Operation

When the relay is switched  the high speed unit will operate inside 4 milliseconds followed

shortly after by the MVAA. The outgoing contacts of the two units are in parallel so to give

high speed and the breaking capacity. By using a low value resistor in parallel the 10 uF

capacitor discharge is overcome. As the MVAA 11 operates it switches out the MVAA16

and parallel resistor to lower the burden to an acceptable level.

Results

Pick up range: 87.5-  137.5V

Pick up time: 4 milliseconds  over voltage range

Drop off time: 15 milliseconds

Initial Burden  180 watts at 137.5 volts for 4 milliseconds  reducing  to 65 watts and finally

6.8 watts after 15 milliseconds.

The MVAJ31 is built on similar lines to the MVAA 16 and followed by an MVAA11 using a

mixture of standard  and heavy duty contacts. In order to meet the capacitor discharge

test some resistors and internally  wired contacts  have been added.

Case Size

The relay may be housed in either  MIDOS  size 3 or size 4 cases. The heavy duty contacts

are as for the MYAA II  so the same contact duties can be claimed.  All other outgoing

contacts  are as standard  MVAAs.

Key Benefits

• High speed operation

• High and low burden alternatives

• Models surge proof against high capacitance discharge currents in the dc supply system,

are available

• Control relays immune to AC can be supplied

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.