Siemens 7SA511 manual Emergency Overcurrent Protection, Power Swing Protection optional

7SA511 Line Protection RelayProduct Description

2.4.2 Emergency Overcurrent Protection

During periods when the line secondary voltage signal is not available, the relay can be used as a two-stage, definite-time, overcurrent protection device. You can also program the relay to automatically change over to the overcurrent mode for “emergency” service following detection of VT circuit failure. The VT failure is detected by the relay’s internal monitoring and plausibility checks. External detection of VT failures may be input to the relay via a binary input.

2.4.3 Power Swing Protection (optional)

Power swing protection is an optional function in 7SA511 relay models that use the polygonal impedance fault detection scheme (model number 7SA511*-**A52***1/3). There are two ways you can program the relay to respond to a detected power swing.

1.Blocking. The distance protection tripping function may be blocked for the duration of the power swing.

2.Tripping. Tripping may be initiated following the detection of a power swing outside the defined stability limits.

2.4.4Pilot Protection

The 7SA511 relay provides pilot protection for fast, selective clearance of faults over the complete line. You can choose from the following pilot protection schemes:

Permissive underreach transfer tripping(PUTT) with nondirectional fault detection Permissive underreach transfer tripping with directional overreach zone Z1B) Permissive overreach transfer tripping (POTT)with overreach zone Z1B Directional comparison with fault detection

Unblocking with zone Z1B Blocking mode with zone Z1B

￿Directional pilot wire mode

Reverse interlocking (bus protection)

The pilot protection signal interface is implemented by assigning appropriate logical functions to a signal relay (transmitter) and a binary input (receiver).

2.4.5High-Sensitivity Ground Fault Protection for Ungrounded Systems (optional) In systems having an isolated neutral or a neutral grounded through an arc suppression coil, single-phase ground faults will not be detected by the short circuit protection function because of the minimal flow of ground fault current. The optional ground fault protection function for ungrounded systems recognizes, and when possible, locates the fault. Ground fault protection for ungrounded systems (relay models 7SA511*-**A5*-1***) includes the following functions.

The relay detects (picks up) the ground fault by monitoring the displacement voltage.

￿By measuring the phase-to-ground voltages, the relay determines the faulted phase. The direction of the ground fault (residual) current is determined by high accuracy, real, and apparent component measurement.

2-10 July 27, 1995