Basler Electric BE1-87B - Manual (Page 69)

SECTION 5
• TESTING
CT Circuit Testing
The CT Diagnostic Test Source, available with the BE1-87B, provides a simple way to test and verify that
the CT input circuit is not shorted. The Test Source assembly (Basler P/N 9282300014) consists of a
120/240 volts to 30/60 volts, 50 VA transformer with a 100 ohm, 50 watt resistor is series with the
common lead of the secondary (Figure 4-20). All components are contained in a metal enclosure and
have screw-terminal connections. The CT Test pushbutton on the relay front panel is used to apply the
test voltage. This pushbutton is standard on all BE1-87B relays. The output of the CT Diagnostic Test
Source should be connected between relay terminals 7 (COM) and 10 (TEST).
The voltage supplied by the CT Diagnostic Test Source is derived from an isolation transformer to avoid
applying multiple grounds to the CT circuit. The input to the Test Source is dual rated to meet the user’s
nominal secondary station service voltage rating. The output of the Test Source can be connected for 30
volts or 60 volts, depending on the requirement of the application.
Operating Principle – CT Circuit Testing
The CT Diagnostic Test Source provides convenient verification of CT circuit integrity. By applying an
external test voltage (30 Vac or 60 Vac) through a 100 ohm, 50 watt resistor to an energized CT circuit,
the Test Source causes a low-level current to flow through the effective parallel impedance of the CTs
and the relay input impedance. Test voltage is applied by pressing the CT Test button (front panel) for
one minute or until the front panel CT OV LED lights. Phases should be tested individually; faulty results
may occur if more than one phase is tested simultaneously. In a healthy CT circuit, the resulting voltage
drop will light the CT OV LED and close the Alarm output contacts (terminals 13 and 14). If a CT or
current circuit cable is shorted when the test voltage is applied, all of the voltage will be dropped across
the Test Source resistor and the CT OV LED and Alarm output will not operate.
Section 2, Application, CT Test Circuit Calculations provides information about determining the
appropriate relay settings and Test Source voltage to use for CT circuit testing.
Security Considerations – CT Circuit Testing
The voltage required to gate the BE1-87B SCRs is two times V DIFF or 300 volts as in the CT test
example of Section 2, Application, CT Test Circuit Calculations. By maintaining the test voltage at
approximately 1.5 times V ALARM or 30 volts as in the example, a transient of 10 per unit would have to
occur to gate the SCRs.
If a severe voltage transient occurs while the CT Test button is being pressed, it would have to last
several milliseconds to overcome filtering delays. The probability of this combination of events occurring
is very low. But, if a severe transient should turn on the SCRs during the test, a current fault detector set
above the unhealthy current flow provides a second level of security. Therefore, CT testing offers no
threat to the security of the differential scheme.
Acceptance Testing
The following procedures should be used for acceptance testing the BE1-87B relay. The only difference
between testing a single-phase model and three-phase model is the test connections for phases B and C
of the three-phase model. Refer to the connection diagram associated with each test. Also refer to
Figures 3-1 through 3-3 for the location and description of the relay controls and indicators. Figure 5-1
shows the side view of the M1 or 19” Rack-Mount and S1 relays with the individual circuit boards
identified. Figure 5-2 illustrates the use of the circuit board extender card.
9282300990 Rev P BE1-87B Testing 5-1