Energy saving on the crusher drives at NTPC Badarpur.

The problem

NTPC Badarpur runs three coal crushers, each driven by a 360 KW / 1470 RPM motor. The crushers were coupled through rotating-body type scoop-controlled fluid couplings (type SCR-24, size 26) — and the plant faced a string of perennial problems with them.

• The automatic scoop-tube control malfunctioned: the tube would not return to the 0% position on starting, so the desired fast decay of starting current was lost.
• The couplings were large-diameter and very heavy. Operators were wary of going near them — in the past, one coupling had broken away and flown off, causing heavy damage.
• That heavy mass, large diameter and the alignment difficulty inherent to the SCR design left vibration and noise levels very high.
• A water-cooled oil cooler meant a dedicated water supply and pipework had to be provided and maintained.
• The couplings needed frequent maintenance, ran at high cost and demanded a large inventory of spares.

The brief

NTPC wanted a simpler coupling that needed no maintenance and put an end to these problems. At the same time, they did not want to alter the existing base frame or shift the motor from its existing location — so any solution had to fit the drive exactly as it stood.

The Fluidomat solution

Fluidomat studied the problems and the existing drive set-up and offered an effective answer: the displaceable delayfill coupling, model HFD-10B. It was custom-built to be accommodated in the large shaft-to-shaft distance left by the SCR coupling, so neither the base frame nor the motor had to move. NTPC purchased one coupling and installed it on 12 June 1999.

The outcome

On running the HFD-10B coupling, NTPC observed an immediate and comprehensive improvement.

• Motor starting is soft and starting current decays very fast.
• Acceleration of the crusher is very smooth.
• Vibration and noise came down substantially, well within desired levels.
• The complicated set-up required for the SCR coupling was eliminated — no water supply needed.
• The coupling is operator friendly; staff no longer fear approaching it for observation.
• Simple in design, it needs far fewer spares and the operating cost is much lower.
• Being radially displaceable, it is easy to fit and remove.
• The coupling is maintenance free.
• As a bonus, the motor's running current fell from 32 A to 30 A — an almost 6% energy saving, substantial enough to pay back the HFD-10B coupling cost in a short period.

With the success of the first HFD-10B, NTPC Badarpur removed the remaining two SCR couplings and fitted Fluidomat couplings on all three crushers — and they have been in operation successfully ever since. Clients facing problems with SCR couplings are welcome to refer to us for a solution.