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Subject: Large Power Variable Frequency Drives for Boilers in Thermal Power Stations

Date: 11/03/03 at 10:47 PM
Posted by: Hemant Sawarkar
E-mail: nelcoma_engg@vsnl.net
Message Posted:

Reliable Variable Frequency Drives are now available for handling very large power and medium Voltage to control the speed and hence the flow of large Induced Draft (ID), Forced Draft (FD) Fans, Boiler Feed Water Pumps (BFPs), Chilled Water Pumps, Secondary Coolent Pumps, Condensate pumps etc for large sized boilers of coal or oil fired thermal power stations.

Conventionally, the large fans use inlet vanes, or outlet dampers or variable speed hydraulic couplings, which are energy consuming devices, and hence reduce the efficiency of the overall system. The hydraulic couplings also provide maintenance headaches to the user. The hydraulic or fluid coupling operating in variable speed operation consume lot of energy and its efficiency drops down to 45% at 30% speed of the fan or a pump.

Conventionally, the LCI type variable frequency drives have been used for many large power applications. with the synchronous motors. However, the LCI drives technology has been on the verge of obsoletion. More advanced medium voltage drives are now available at a competitive price tag, which use conventional standard squirrel cage induction motor.

Energy savings in the auxiliaries of the thermal power plant is now a days of great concern to the energy producer, becuase every electrical unit saved, can be sold.

Variable Frequency Drives are now available, which can deliver variable voltage, variable frequnecy in the range from 2.3kV to 6.6kV, for a frequency of 0 Hz to 300 Hz. These are avaialble from 200kW to 40,000kW power range for the induction motors.

These VFDs are very reliable, and can be provided with hot redundancy in the main power circuit of the drive. These provide a very high efficiency at 96.5% of drive in to drive out. The power factor for the VFD is maintained better than 0.95 over entire speed range at all loads. The mains supply side harmonics generated are very low, because of its large number of rectification number. This means for a typical 6.6kV output drive, the VFD provides 36 pulse rectification, which totally meets IEEE519-1992 specifications for both group and individual current and voltage harmonics, irrespective of the mains power line short circuit parameters.

The motor side harmonics are very much on lower side, because of its multi-PWM stepped sine pattern generators, which gives near sine waveform for current as well as for voltage.

These featues make these drives perfectly suitable for retrofit applications, where the existing motor can be used with these VFDs.

for more details, please contact -
Hemant Sawarkar
Manager Marketing
High Power AC Drives Group
Mahakali Caves Road, Chakala, Andheri (east)

Telephone +91-22-56796969 extension 269
Fax +91-22-56791919
Mobile +91-094224-73795

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