Читать книгу Practical Power Plant Engineering - Zark Bedalov - Страница 80

Each major plant will need some standby power (see Figure 2.14). Often, it is called “essential power” in comparison to the “emergency power,” which usually comes from station batteries. The essential power is needed to ensure safety of the personnel and to provide for an orderly plant shutdown as well as quick power restoration and plant operation following a power outage. The standby power must be sized to feed all the critical (essential) loads: part of lighting, DC chargers, plant control system, UPS, heating, and heat tracing where necessary. Also, to power the sensitive process loads and products, which must not be let to harden or freeze up following a power failure.

As noted earlier, the critical path circuit breakers will be provided with latched contactors or circuit breakers that will remain turned on upon a loss of power to be ready to restore the power supply to the essential loads in anticipation of the DG starting up and feeding the essential load. All the other loads will be turned off and wait for the normal power to be restored and for the plant control system to gradually restore power to all the plant services. To insure, the standby power plant is not overloaded during a plant outage, the plant motor loads will drop out or be forced to shut down during a loss of normal power and be held open until restarted by the plant control system onto the normal power.

Standby units often are purchased as packaged standardized container units, with acoustic enclosures, fully wired, and ready for operation. The standby plant must be designed to be black start capable. The engines will be provided with DC batteries for starting.

The cost of the diesel equipment is proportional to its speed as much as it is to its power. Standby power typically uses 1200 or 1800 rpm, 1–1.5 MW units. The standby unit will be provided with provisions to be tested and synchronized/connected to the plant distribution system during the normal operation to prove its standby duty readiness on a weekly basis.

Figure 2.14 Standby generator.

A loss of voltage for three seconds is a good criterion for initiating a start‐up of standby units. Within 15 seconds, the unit will be running and be ready to “synchronize” on the plant dead bus and pick up the load. More on diesel engine generation in Chapter 20.

The plant control system must be operated on the emergency power (DC battery supply) to ensure proper power restoration is initiated after the normal power source is restored. The power restoration procedure (back from a failure) and switching off the standby generation in this type of plants is typically a manual procedure.

The principal loads requiring back up of essential power are

 Camp, including water supply (partial)

 DC chargers to power UPS and plant batteries

 Thickeners, rakes, and U/F pumps

 Instrument air

 Fire detection system

 Lighting (partial)

The standby generators will make use of the plant electrical infrastructure (distribution system) to deliver standby power to all parts of the plant.

The camp will include two 0.5 MW standby units operated at 480 V with synchronizing capability to feed the miscellaneous critical and essential loads. The emergency power will be tied directly to the camp distribution system via ATSs, which will respond to initiate the standby generation following a loss of the principal power received over the 13.8 kV overhead lines.

The camp standby gensets and the switchboard will be trailer‐mounted, placed adjacent to the camp main switchboard.