Commissioning; Description Of Relay, Calculation Of Setting And Commissioning Preliminaries - GE MFAC 14 User Manual

Publication R6001 is a leaflet on the modular integrated drawout system of
protective relays.
Publication R6014 is a list of recommended suppliers for the pre-
insulated connectors.
Section 2.

COMMISSIONING

2.1

Description of relay, calculation of setting and commissioning preliminaries

2.1.1 Description of MFAC 14/MFAC 34
This is a voltage operated relay having seven equally spaced settings of
15–185 volts, 25–175 volts, 25–375 volts or 100–400 volts which may be selected
by means of a plug bridge.
The relays may be used for any type of high impedance circulating
current protection.
2.1.2 List of abbreviations.
I = Current transformer exciting current at relay setting voltage (referred to the
E
CT secondary current)
I = Maximum value of primary through fault current for which protection must
F
remain stable.
I = Maximum value of primary fault current for internal fault.
FM
I = Primary current for operation of protection.
P
I = Relay operating current.
R
I = Current in shunt resistor at relay setting V
SH
N = Turns ratio of current transformer.
n = No. of current transformers in parallel with relay.
R = Secondary resistance of current transformer.
CT
R = Lead resistance between furthest current transformer and relay
L
connection point.
R = Relay impedance.
R
R = Value of shunt resistor.
SH
V = The theoretical voltage which would be produced across the relay circuit
F
under internal fault condition.
V
F
V = Knee point voltage of current transformer.
K
V = Peak voltage across relay circuit under maximum internal fault conditions.
P
V = Minimum setting voltage. (calculated)
S
V = Relay setting voltage.
R
2.1.3 Calculation of relay setting.
The minimum setting voltage to ensure stability is
≥
V
S
The relay plug setting voltage V
= I (R + 2R +
FM CT L
R ) N
R
(R + 2R )
I
F CT L
N
R
.
R
must be set to the nearest tap above V
10
.
S