Guardian Technologies 4390, 4456 TEST 2- CHECK AC OUTPUT VOLTAGE, Section, Diagnostic Tests, Part

SECTION 2.4

DIAGNOSTIC TESTS

PART 2

AC GENERATORS

TEST 2- CHECK AC OUTPUT VOLTAGE	current units with air-cooled engine, "field boost"
	current flow is available to the rotor only during
DISCUSSION:	engine cranking.

Avolt-ohm-milliammeter (VOM) may be used to check the generator output voltage. Output voltage may be checked at the unit’s main circuit breaker terminals. Refer to the unit’s DATA PLATE for rated line-to-line and line-to-neutral voltages.

DANGER: USE EXTREME CAUTION DURING THIS TEST. THE GENERATOR WILL BE RUNNING. HIGH AND DANGEROUS VOLTAGES WILL BE PRESENT AT THE TEST TERMINALS. CONNECT METER TEST CLAMPS TO THE HIGH VOLTAGE TERMINALS WHILE THE GENERATOR IS SHUT DOWN. STAY CLEAR OF POWER TERMINALS DURING THE TEST. MAKE SURE METER CLAMPS ARE SECURELY ATTACHED AND WILL NOT SHAKE LOOSE.

PROCEDURE:

1.With the engine shut down, connect the AC voltmeter test leads across the Wires 11 and 44 terminals of the generator main circuit breaker (see Figure 1). These connections will permit line-to-line voltages to be read.

2.Set the generator main circuit breaker to its OFF or "Open" position. This test will be conducted with the generator running at no-load.

3.Start the generator, let it stabilize and warm up for a minute or two.

4.Take the meter reading. On unit's having a rated line-to- line voltage of 240 volts, the no-load voltage should be about 242-252 volts AC.

5.Shut the engine down and remove the meter test leads.

RESULTS:

1.If zero volts or residual voltage is indicated, go on to Test 3.

2.If the voltage reading is higher than residual, but is lower than the stated limits, go to Test 11.

3.If a high voltage is indicated, go on to Test 11.

NOTE: "Residual" voltage may be defined as the voltage that is produced by rotor residual magnetism alone. The amount of voltage induced into the stator AC power windings by residual voltage alone will be approximately 2 to 16 volts AC, depending on the characteristics of the specific generator. If a unit is supplying residual voltage only, either excitation current is not reaching the rotor or the rotor windings are open and the excitation current cannot pass. On

TEST 3- TEST EXCITATION CIRCUIT

BREAKER

DISCUSSION:

Unregulated excitation current is delivered to the voltage regulator from the stator excitation (DPE) winding, via Wire 2, an excitation circuit breaker (CB2), Wire 162, and Wire 6. If the excitation circuit breaker has failed open, excitation current will not be available to the voltage regulator or to the rotor. Stator AC power winding output will then be reduced to a voltage that is the product of residual magnetism alone.

PROCEDURE:

1.With the generator shut down for at least two minutes, locate the excitation circuit breaker in the generator panel. Disconnect wires from the breaker, to prevent interaction.

2.Set a volt-ohm-milliammeter (VOM) to its "R x 1'scale and zero the meter.

3.Connect the VOM test probes across the circuit breaker terminals. The meter should read CONTINUITY.

RESULTS:

1.Replace circuit breaker if defective (meter reads “OPEN”). Then proceed to Test 4.

2.If circuit breaker is good, go on to Test 4.

Figure 2. Excitation Circuit Breaker

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