Megger SR-98 - Page 66

60
Formula for Westinghouse Type HU Relay % 2 nd Harmonic Restraint:
%
Harmonic Restraint = __1.2267 * 2 nd Harmonic_Current_ * 100
√
(
Fundamental)
2
+ (2nd Harmonic)
2
For example, a Westinghouse type HU, harmonic restraint relay, set for a 15 %
harmonic restraint, might have typical values of 1 Ampere 2 nd Harmonic Current
(Slave Unit) and 8.2 Amperes Operating Current (Master Unit). The calculation
would look like the following,
%
Harmonic Restraint = __ 1.2267 * 100
⇒
14.85 %
√
(
8.2)
2
+ (1)
2