Saturday, June 13, 2009

TYPICAL APPLICATION OF DUAL PRIME SOURCE OPTION FOR ON-SITE POWER SYSTEMS

In many critical applications it is imperative that the prime power system operate without fail. As a result, specifying engineers may require two on-site power generation plants to insure that an alternate power source will be available. In this scenario the Communication Towers Shelters Dual Prime Source option is ideally suited.

Dual prime operation is typically utilized for installations where no utility power is available thereby requiring two generator sources to supply a site load. This option allows either source to be selected as the “preferred” or “prime” source. The preferred selected generator would be operating on load, with the alternate “standby” generator stopped.
When the “preferred” generator source fails, the transfer switch will automatically transfer to the alternate generator supply if available.

As in a conventional transfer switch, the Dual Prime Source Transfer Switch is designed to transfer a load between two power sources with one power source being designated as the Preferred Source (Genset No.1) while the other is designated as the Alternate Source (Genset No.2).
In this system, selection of the Preferred Source (Genset No.1 or Genset No.2) is accomplished by a door mounted selector switch provided. In the Automatic mode, a time clock alternates which power source is the Preferred Source at a set time or multiple times during a seven day period.
If a failure of the Preferred Source occurs, the transfer switch will start the Alternate Source and transfer the load to it. When the faulted Preferred Source is returned to service, the transfer switch will then retransfer the load back to the Preferred Source power.

The Dual Prime Source accessory for a Generator to Generator system provides the following accessories and/or descriptions:

CYCLIC OPERATION ATS – PLC or Analog Approach (Contactor or Breaker Type)
a. 1 or 3 phase close differential over/undervoltage sensing on both sources
b. Time Delay Control timer for both sources to allow engine to attain speed
c. Engine Maintain Timer for both sources to allow engine cool down period
d. Preferred Source Selector switch to choose the preferred (Genset No.1 – Auto -
Genset No.2) source with “OFF” option
e. Pilot lights to indicate the source to which the load is connected and FAULTS
f. Fault RESET button and TEST button for LAMPS (Busted)
g. A fourteen day or preferred time clock which will automatically alternate the
generator set selected as the Preferred Source at a chosen interval to ensure even
running time on both engine generator sets. (Automatic operation only)
h. ATS & Generator Remote Controlling, Monitoring and Communication Capability
1. TCP/IP over Ethernet Connectivity
2. Supports SNMP v1, SNMP v2 Protocols
3. Alarm and Status functions

Normal operation would require one generator continuously on load with the second generator operating as a “standby” unit.
Dual prime logic allows an operator to select which source is “preferred” (i.e. either source may be selected as preferred or Automatic Mode), therefore, the opposite source will act as the “standby” source.
A PREFERRED SOURCE selector switch is provided for an operator to manually select a “Preferred” operating source. The “Preferred” selected source will continuously operate on load with an engine start signal maintained. The non-selected unit (standby) will remain in the OFF condition. The “standby” unit will be signaled to automatically start the engine and transfer on load (following its engine start and warm-up delay period) should the “Preferred” operating unit fail. When the “Preferred” selected unit is returned to normal operating status, the load will automatically retransfer back to the “Preferred” selected source.
If the PREFERRED SOURCE selector switch is turned to the non-operating unit, the load will automatically transfer to this new “Preferred” source once the engine has started and warm-up period has expired. The originally selected prime unit will continue to operate for its cooldown period (0-1800 sec. adjustable), and then stop.

Note: For automatic operation, both engine control panels must be set for the automatic mode of operation.

When the selected sources supply voltage drops below a preset nominal value (70 -
100% of rated adjustable) on any phase, an engine start delay circuit will be initiated to the opposite (standby) sources engine control and the transfer to the sleeted source signal will be removed (i.e. contact opening). Following expiry of the engine start delay period (0-60 sec. adjustable) an engine start signal (contact closure) will be given. Once the opposite (or standby) engine starts, the transfer switch controller will monitor the generator’s voltage and frequency levels. Once the generator voltage and frequency rises above preset values (70 - 100% nominal adjustable), the engine warm-up timer will be initiated. Once the warm-up timer expires (0-1800 sec. adjustable), the transfer signal (contact closure) will be given to the transfer switch mechanism. The load will then transfer from the prime selected source to the opposite (standby) source via motor driven mechanism.
The “standby” will continue to supply the load until the prime selected source has returned and the retransfer sequence is completed as follows:
When the prime selected source voltage is restored to above the preset values (70 - 100% of rated adjustable) on all phases, then the load will retransfer from the “standby” source back to the prime source.
An engine cooldown timer circuit will be initiated once the load is transferred from the “standby” generator. Following expiry of the cooldown delay period (0-30 min. adjustable), the engine start signal will be removed (contact opening) to initiate stopping of the “standby” generator set.