Siemens 7SA511 manual Voltage Subsystem, Distance Protection Overview

7SA511 Line Protection Relay Reference A

The microprocessor performs all impedance and overcurrent calculations and makes all protection logic decisions. The microprocessor also provides the following functions:

Filtering and formation of the measured quantities

Continuous calculation of the values required for fault detection Determination of the faulted phases and the direction of faults Scanning of limit values and time sequences

Controlling of signals and sequences for pilot protection, automatic reclose, etc. Decision for tripping circuit breakers

￿Storage of instantaneous current and voltage values during a fault Storage and issue of messages and fault data for fault analysis

Binary inputs are isolated through optical couplers. Outputs include trip contacts, signal contacts, LEDs, and an alphanumeric LCD on the operator panel. You can program the binary inputs, output contacts, and LEDs as discussed in Chapter 5, “Programming the Relay.”

Using the operator panel keypad and LCD, you can read or change the system, protection, and relay configuration settings, access and read the relay’s measured values, and review the target history logs for the last three faults. This interaction with the relay can also be accomplished using DIGSI“software on a personal computer connected to the serial interface port on the operator panel (refer to Figure 2-1 in Chapter 2, “Product Description”).

An integrated DC-to-DC converter supplies multiple voltages to the relay subsystems as follows:

Voltage		Subsystem
+24	V	Output relays
15	V	A/D converters
+12 V		EEPROMs
+ 5	V	CPU and associated logic

The relay can withstand a loss of input supply voltage for 50 milliseconds (VH ￿110 V) without going out of service (refer to Reference D, “Specifications”).

A.2 Distance Protection Overview

Distance protection is the main function of the 7SA511 relay. Depending on the model, you can choose from three different fault detector combinations to ensure the optimal protection for the protected system. The fault detector combinations can be any one of the following:

Overcurrent (7SA511*-**A51-****)

Overcurrent, Voltage-controlled overcurrent, and Polygonal impedance (7SA511*-

￿**A52-****)

Overcurrent and Voltage-controlled overcurrent (7SA511*-**A53-****)

In addition to the above fault detectors, an independent distance-to-fault function is provided.

July 27, 1995 A-7