Section 3 — Operation
Guardian
3.4SEQUENCE OF AUTOMATIC
OPERATION
The generator’s control panel houses a control logic circuit board. This board constantly monitors utility power source voltage. Should that voltage drop below a preset level, circuit board action will signal the engine to crank and start. After the engine starts, the circuit board signals the transfer switch to activate and connect load circuits to the standby power sup- ply (load terminal lugs T1/T2 connect to terminal lugs E1/E2).
Upon restoration of utility source voltage above a pre- set level, generator circuit board action signals the transfer switch to transfer loads back to that power supply. After retransfer, the engine is signalled to shut down.
The actual sequence of operation is controlled by sensors and timers on a control logic circuit board, as follows:
A.Utility Voltage Dropout Sensor
•This sensor monitors utility source voltage.
•If utility source voltage drops below about 70 per- cent of the nominal supply voltage, the sensor energizes a
•Once the timer has expired, the engine will crank and start.
B.Engine
•This mechanism lets the engine warm up for about 10 seconds before the load is transferred to the standby source.
C.Standby Voltage Sensor
•This sensor monitors generator AC output volt- age. When the voltage has reached 50 percent of the nominal rated voltage, transfer to standby can occur.
D.Utility Voltage Pickup Sensor
•This sensor monitors utility power supply volt- age. When that voltage is restored above 70 per- cent of the nominal source voltage, a retransfer time delay starts timing.
E.Retransfer Time Delay
•This timer runs for about 15 seconds.
•At end of a
•Retransfer to utility power source then occurs.
F.Engine
•When the load is transferred back to utility power source, the engine
•The timer will run for about one minute, and the generator will then shut down.
3.5MANUAL TRANSFER OPERATION
3.5.1 TRANSFER TO GENERATOR POWER SOURCE
To start the generator and activate the transfer switch manually, proceed as follows:
1.Set the generator’s Auto/Off/Manual switch to OFF.
2.Set the generator’s main circuit breaker to its OFF (or open) position.
3.Turn OFF the utility power supply to the transfer switch using the means provided (such as a utility main line circuit breaker).
DANGER
Do not attempt to activate the transfer switch manually until all power voltage supplies to the switch have been positively turned off. Failure to turn off all power voltage supplies may result in extremely hazardous and possibly fatal electrical shock.
4.Use the manual transfer handle inside the trans- fer switch to move the main contacts to their “Standby” position, i.e., loads connected to the standby power source (Figure 3.2).
Figure 3.2 – Manual Transfer Switch Operation
5.To crank and start the engine, set the Auto/Off/Manual switch to MANUAL.
6.Let the engine stabilize and warm up for a few minutes.
7.Set the generator’s main circuit breaker to its ON (or closed) position. The standby power source now powers the loads.
Generac® Power Systems, Inc. 15