Description Of Operation; Settings - Siemens 7SG164 Ohmega 400 Series Manual

1.6.2 Description of Operation

1.6.2.1. Power Swing Detection.
The relay uses 2 zones of protection to detect a power swing condition, defined as the inner and the
outer zones. Each of these zones consists of a phase to phase fault comparator applied to the Yellow-
Blue phase. Upon operation of the outer zone, a timer is started. If the time between the operation of
the outer zone and the inner zone is greater than the relay PSD Transit time, the relay will raise the
power swing alarm.
The reach of the power swing detection zones are set in terms of impedance for the inner reach. The
outer reach is then set by a multiplying factor, usually 1.5 times the inner reach.
ZPSB(Outer) = k. ZPSB(Inner)
The inner reach should be either equal to or just above the furthest reach setting of the relay, so that
all zones of the relay are contained completely within the inner power swing detection zone. A check
should also be made on the outer reach with reference to the maximum feeder load. The outer reach
should not encroach upon the load condition under any circumstances. This check is best carried out
by inspection – if necessary sketching out the characterstics to ensure correct co-ordination. The
blinders can be applied to prevent load encroachment if this is a possible problem.
1.6.2.2. Power Swing Blocking.
Once a power swing has been detected it is often desirable to prevent operation of the relay during a
power swing condition. The relay can be set to block operation of any combination of protection zones
within the relay.
Faults can occur during power oscillations, so it is necessary to provide a mean of distinguishing
between a power swing and a genuine fault condition. Because a power swing condition is always a
balanced three-phase condition, the relay can use the level of negative phase sequence current on the
system to determine between these two conditions. Under balanced conditions, an untransposed
transmission system can produce negative phase sequence currents of up to 14% of positive phase
sequence current. Under fault conditions, however, the level of negative sequence current will be
much higher. Thus, when the negative sequence current exceeds 25% of the positive sequence
current, the power swing blocking will be removed, allowing the relay to operate.

1.6.3 Settings.

Power Swing detector Enable/ Disable
PSD Zone Blocking Zone 1 Zone 2 Zone 3 Zone 4
PSD Shape Circular / Rectangular
PSD Blinders Enable / Disable
Inner Forward Impedance 0.1-250 (24)
Inner Reverse Impedance 0.1-250 (8)
Inner Blinder Forward 0.1-250 (16)
Inner Blinder Reverse 0.1-250 (16)
Multiple (Outer Impedance) 1.05-2.50 x (1.5)
PS Timer 0-1000ms (50)
Status Inputs: N/A
Relay Outputs: POWER SWING ALARM
©2010 Siemens Protection Devices Limited
7SG164 Ohmega 400 Series Impedance Functions
Chapter 2 Page 16 of 21