Application example
750/760 Quick Reference Guide
41
Neutral protection settings
1.
Time Overcurrent 1 (function 51N1):
•
Curve shape = Moderately Inverse
•
Pickup = 120 A
•
Multiplier = 10
2.
Instantaneous Overcurrent 1 (function 50N1):
•
Pickup = 120 A
•
Phases required = Any two
•
Delay = 0 seconds
3.
Instantaneous Overcurrent 2 (function 50N2):
•
Pickup = 2000 A
•
Phases required = Any two
•
Delay = 0 seconds
The above data will be used to configure the relay protection. In this example, the relay will
be used for Phase and Neutral Overcurrent protection only; that is, functions 51P1, 50P1,
50P2, 51N1, 50N1, and 50N2.
In this manual, Neutral Overcurrent is to the residual current, calculated from the currents
measured at the phase CT inputs: terminals G7-H7 for phase A, G8-H8 for phase B and G9-
H9 for phase C. Since it is a calculated value, it cannot be used to generate oscillography.
Ground Overcurrent refers to the current measured at terminals G10-H10, or at terminals
G3-H3 for Sensitive Ground Overcurrent, when the relay is fitted to measure sensitive
ground current.
You should now be familiar with maneuvering through and editing setpoints. As such, we
will now limit our discussion to just the values that must be programmed, in order to meet
the requirements of the example application. Any setpoints not explicitly mentioned should
be left at the factory default value.
S2 System setpoints
The S2 setpoints page contains setpoints for entering the characteristics of the equipment
on the feeder electrical system. In our example, these characteristics are specified under
the Power System Data and Instrument Transformer Data headings in the previous sub-
section. From this information and the resulting calculations, program the page S2
setpoints as indicated.
For current transformers, make the following change in the
S2 SYSTEM SETUP
Z
CURRENT
SENSING
setpoints page:
PHASE CT PRIMARY
:
“600 A”
Since the example does not contemplate a ground CT, the setpoints for
GND CT PRIMARY
,
and
SENSTV GND CT
can be left unchanged. For additional information refer to Chapter 5
of the 750/760 instruction manual.
For voltage transformers, make the following changes in the
S2 SYSTEM SETUP
ZV
BUS VT
SENSING
setpoints page:
VT CONNECTION TYPE
: “Delta”
NOMINAL VT SECONDARY VOLTAGE
: “115.0 V”
Summary of Contents for 750
Page 2: ......
Page 39: ...Application example 750 760 Quick Reference Guide 35 Figure 17 Typical three line diagram...
Page 41: ...Application example 750 760 Quick Reference Guide 37 Figure 19 Typical control diagram...
Page 42: ...Application example 38 750 760 Quick Reference Guide Figure 20 Typical breaker control diagram...
Page 43: ...Application example 750 760 Quick Reference Guide 39 Figure 21 Typical relay control diagram...
