2
Features
• Detects voltage circuit failures
• Can be used to switch to an
alternative supply if the main
supply fails
• Compact design
• Mechanically stable
Application
The MVAP 22 is essentially a fuse
failure relay with changeover output
contacts enabling its use for either
voltage selection or fuse failure
protection. A typical application as
a voltage selection relay is the
automatic connection of metering
equipment to an alternative supply if
the normal or preferred supply fails.
As a fuse failure relay it will monitor
the output of a voltage transformer
and give an alarm or disconnect
protection circuits for VT fuse failure.
The relay monitors the three phase
voltage supply and operates if the
supply is interrupted or becomes
unbalanced due to failure of the
voltage transformers primary or
secondary fuses.
Voltage failure detection on
generator VTs
The Type MVAP 22 relay can be
applied to provide an equivalent
function to the voltage balance relay
by using one MVAP 22 per voltage
transformer and connecting the
output contacts of the two MVAP 22
relays as shown in Figure 3.
The relay combination can be used
to block relays or other devices that
will operate incorrectly when a
voltage transformer primary and/ or
secondary fuse( s) blow or to give
an alarm for the faulty voltage
transformer.
Each relay is supplied from its own
voltage transformer and will detect
blown fuses in either the primary or
secondary windings of the voltage
transformer or if the voltage supply
becomes interrupted.
In the event of a generator short
circuit causing the voltage supplied
to the relays to become appreciably
unbalanced the relays will operate,
but the trip circuit via the generator
protective relays ( ie., devices 21,
32 and 40) will be maintained
through the normally closed contacts
on the two changeover contacts
A– 1 and B– 1, and an alarm will be
prevented via the normally closed
contacts A– 3 and B– 2.
Failure of any voltage transformer
supply will cause operation of the
appropriate MVAP 22 relay and
block tripping of the associated
generator relays which may be
adversely affected by the loss of
voltage supply via contacts A– 1 or
B– 1 and give an alarm via A– 2 or
B– 3.
Description
Two attracted armature units are
employed as shown in Figure 3.
Unit A is fed from a resistance/
capacitance network which under
healthy conditions with negligible
harmonics has zero output.
An operating voltage appears
across the coils of unit A when the
secondary voltages become
unbalanced due to loss of any one
primary or secondary phase. Unit B
has six changeover contacts for
voltage selection and is normally
energised via the normally closed
contact on unit A from two phases
of the supply. Unit B drops off on
operation of unit A, on complete
loss of supply, or on loss of two
primary or secondary phases.
If three limb core type star
connected voltage transformers are
used, the relay will not operate
correctly if the star points of the
primary windings are connected to
neutral or earth. |
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