MVT 181 is a numerical true RMS single pole relay consists of two
elements. Each element can be selected for under voltage function
or over voltage function or switched off. The characteristics
setting, voltage setting and time multiplier setting are
independently settable for each element and the voltage setting is
in terms of voltage. Hence this relay can be used as a two stage
under voltage or two stage over voltage protection. Multiple Characteristics: There are four operating characteristics for over voltage function
and two operating characteristics for under voltage function. Overvoltage Characteristics: Definite Time Lag (DTL) Long Time Inverse (LTI) Extremely Inverse 1(El 1) Extremely Inverse 2(El 2) Undervoltage Characteristics: Definite Time Lag (DTL) Extremely Inverse 1(El 1) Two elements: Two stage O/V Two stage U/V Or one O/V and one U/V Timer: The relay is provided with two status inputs, one of which is to be
connected across the circuit breaker auxiliary contact 52a. From
this the circuit breaker closed or opened condition is found out.
This information is used to introduce a time delay between
successive switching of the capacitor banks which allows the
capacitor bank to discharge to a safer value after disconnected
from a live network. This timer function is a settable one and its
output (N/O) contact is used in the closing circuit of the circuit
breaker. The completion of this time delay is also indicated by
^TIMER^ LED in the front fascia. In addition the same status input
can be used for Trip circuit supervision also. During other under voltage and over voltage applications this timer
function can be disabled or used as an independent timer function. Trip Circuit Supervision: Pre-closing and post-closing supervision of the trip circuit and
trip supply is possible with this relay. A low value of DC current
is passed through the entire trip circuit to monitor the trip coil,
its auxiliary switch and the associated wiring. One of the status
input is connected across the tripping contact and another status
input is connected across the 52a contact (auxiliary contact of the
circuit breaker) in series with the trip coil. During trip circuit
fail condition the monitoring current flow ceases and the energised
status input drops off and the relay gives a contact output to
indicate this condition. In addition to this contact an LED is
provided in the front fascia to indicate the ^T.C. FAIL^ condition.
A time delay of approximately 400 msecs has been given to avoid
false trip circuit fail indication at the time of normal tripping.
Thus trip circuit supervision is the integral part of the relay. If
this function is not required the same can be put off in the
setting menu. |