Siemens SG8158-00 manual Self-Monitoring Value Supervision, Output Contact Status

Control & Communications

Binary Outputs (7409) displays the output contact status as illustrated in Figure 6.3. The status updates automatically as they change.

Figure 6.3 Output Contact Status

6.10 Self-Monitoring (Value Supervision)

Value supervision refers to the relay’s ability to monitor its own input and measurement functions for problems. The complete chain, from input transformers up to and including the A/D converter internal to the ISGS, is monitored by a plausibility check on the measured values. These checks consist of voltage balance checks, current balance checks, and current summation checks.

Voltage or current balance checks can be performed to detect open or short circuits in the external transformers and their connections. Current summation checks are performed on the instantaneous samples of the A/D converter.

A useful application of the current and voltage balance and monitoring functions is the detection of blown VT fuses. A blown fuse condition can be said to exist when the following conditions are present:

Voltage is present but unbalanced,

AND

current is present but NOT unbalanced.

⎛⎝ V1 > 25 V⎞⎠ AND ⎛⎝ V2 < 0.33 V1 ⎞⎠ AND ⎛⎝ I2 < 0.167 I1⎞⎠ OR ⎛⎝ I1 < 0.1 IN⎞⎠

where V1 = positive sequence voltage I2 = negative sequence current I1 = positive sequence current IN = nominal current (1 or 5 A)

Therefore, a voltage balance alarm in the absence of a cur- rent unbalance alarm is a good indication that a fuse is blown. If a current unbalance alarm were also active, it would indicate the presence of negative sequence current and therefore a fault rather than a blown VT fuse.

3400	Value Supervision
Address	Parameter	Selection
3401	Function V Bal	Enabled or Disabled
3402	Pickup V Bal	40-120 V	(0.1 V steps)
		(default is 100)
3404	Factor V Bal	0.58-0.95 (0.01 steps)
		(default is 0.8)
3411	Function I Sum	Enabled or Disabled
3412	Pickup I Sum	5 A CTs: 0.5-5 A
		1 A CTs:	0.1-1 A
		(0.1 A steps)
3414	Factor I Sum	0.10-0.95 (0.01 steps)
		(default is 0.1)
3421	Function I Bal	Enabled or Disabled
3422	Pickup I Bal	5 A CTs:	0.5-5 A
		1 A CTs:	0.1-1 A
		(0.1 A steps)
3424	Factor I Bal	0.10-0.95 (0.01 steps)
		(default is 0.8)

Voltage Balance

The Voltage Balance function can be enabled or disabled (3401). When enabled, the function monitors the phase volt- ages to see if they are approximately balanced (of equal magnitude). Balance is defined as the ratio of minimum to maximum voltage, where the maximum voltage is the largest and the minimum voltage the smallest of the three voltages determined by the way the relay is connected (line-to-line or line-to-neutral).

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