Motor Control Center

Motor Control centre both of HT & LT description are on the manufacturing anvil.

LT Panel- Motor Controls centre are manufactured keeping in view of The various types of requirements such as:

  1. Steel re-rolling mills
  2. Paper Mills
  3. Cement Mills
  4. Sugar Mills
  5. General Industrial Workshop.

Steel re-rolling mills, cement mills and sugar mills start on high inertia and as such the starting torque will be high using slip-ring motors. So, we manufacture resistance starters of 3, 5 or 7 steps using either stainless steel grids or Nichrome strips for higher horse power and ferry or Nichrome wires for lower HP motors. This can be manufactured up to 10 starts per hour and starting torque up to two times the rated torque. The same is manufactured in fully automatic version.

The same could be started using Liquid rotor starter where a step-less acceleration is possible. Here also the starter can be manufactured up to ten starts per hour using forced cooling. Liquid Resistance Starter could also be offered as speed Controls i.e. possible of an Induction Motor. The same could be supplied for voltage from 415 V 3P 50Cys to 11KV 3P 50 Cys.

The protection offered to higher horsepower motors will be in two steps First, the back up CB providing short circuit and earth fault protection and second the motor protection relay giving overload, locked rotor and single phase protections. HT motors are Controlsled either by an SFU or ACB for stator Controls (S/C to E/F protection) and a vacume contactor with motor protection relay operating on this contactor for other protections. HT starters are additionally provided with surge suppressor, PF improvement capacitor also.

These starters could be hooked up to a computer PLC Controls also. The resistance starters for higher starting duties are provided with suitable extra ventilation suited to temperature rise.

The starter when used as speed regulating may need external super cooling in the form of Cooling Towers or Cold Air Circulation.

The client will have to provide the following details while ordering out the units.

STARTER
VOLTS
V
Starter Volts Amps
Rotar Volts V
Rotar Current Amps
Connected Load in KW/HP

Type of mechanical load connected or starting torque expressed as a percentage of Full Load Torque, whether used as starter or speed Controlsler.

Starting duty :    1 start in two hours   |   2 starts per hour   |  10 starts per hour

If known mention the accelerating Time. Please note that all high horse power motors are allowed to start only once in two hours as per Indian standards and British standards.

Not withstanding the above, the starter will be designed to suit the said duties.

General industrial workshops invariably use cage motors in exception to high horse power compressors and air circulators. Some industries use air circulators with Star-Delta starters by closing the inlet air vent and opening the same after the motor has fully speeded up. Others use slip-ring motors.

Where cage motors are used, the motor is started in three different modes:

  • DOL
  • Auto Transformer Starter
  • Star Delta Starter

Motors when hooked up to electricity supply authority line is governed by limitations of starting current as the high in rush [say 6-8 times the rated current of the motor] which may affect the co-users of the same transformer by way of Voltage Dips. As such clients are allowed to hook up such motor on DOL only up to 5HP [3.7KW]. Beyond this authorities recommend auto transformer starter. In the Auto Transformer starter, the switching media puts in the motor on a low starting voltage during starting and puts in normal voltage during running. This up to 100HP is allowed for an open transition schedule.

Beyond 100HP korendorfer transmission is designed to take care of close transition. From low voltage to normal voltage connection of the motor. This renders the inrush current on the line to Is/square times of turn’s ratio of the Auto transformer over the scheduled DOL inrush. Say if it is used 40% winding during starting the inrush on the main side will be 16% of 6 times the rated current i.e. almost full load current of the motor. Thus both the motor as well as electricity authority’s voltage drop problems are solved at a time. Incase of use of 60% tap the current inrush will be 0.36x6=2.16 times the rated current which is much less than star-delta starting.

But after the 100hp open, transition from low to high voltage is not allowed in view of occurrence of Voltage Doubling Effect during transition. For this the close-transition connections [korendorfer for Connection] is being adopted. This could be offered both on HT & LT versions.

But substation owners of adequate capacities could use even high HP motors say [even 800HP] on DOL. [Both HT & LT]

However up to 100HP still Star Delta starters with open transition is adopted generally, in that case Fully Automatic Star Delta Starters are being supplied with suitable SFU/MCCB/MCB/MPCB back up for S/C Protection. Overload protection forms the part of the starter in the form of MPCB/Thermal Over load relay/Motor Protection Relay depending upon necessity.

Star Delta Starters with Close transition through extra resistors are not in practice but can be instituted in special cases.

DC motor Starters: DC series /Compound/Shunt motor starters can be supplied wherever needed.

Wherein details such as :

  • Rated Voltage of DC motors
  • Rated Full Load Current of DC motors
  • Field Current [In case of Shunt motor]
  • Field Voltage [In case of Externally Fed Shunt Motor]
  • Starting Torque/Full Load Current
  • Starting Time –If known

 

    • DC Shunt Motors could be started with motorized dimmer stats also wherever needed in place of motorized or manually regulated resistances. However step selecting resistance during starting can also be provided for on special request (for external power supplied field).
    • Cage motors when started with variable Frequency drives can also be supplied with or without incoming/outgoing series reactors with Bypass DOL.FASD Starters. In case of Bypass Starter Provision of total Isolation of VFD on both sides will be made by suitable contactors. The same contactor used in by pass delta connection could also be used for connections in motor in delta for VFD.
    • Cage motors when started by Pole Changing device can also be provided in the form of change over pole pickup arrangement with common protection.
    • Forward-Reverse Starters can be provided by electrically and mechanically interlocked contactor arrangement by providing protection on common side.
    • All the above starters can be made on HT & LT versions

  • Synchronous Motors when started as slip-ring motor by the help of Pole Face windings can also be supplied for starting as slip-ring motor and running a synchronous motor by injecting DC to poles.
  • After motor speed picks up in this shortened Pole Face winding acts as damper winding.

Starters for such motors could be supplied. Details necessary will be:

STARTER Volts
Cycles
3Phases
Starter Current   Amps
Pole Face winding Voltage (RA)   Volts
Pole Face winding Current (RV)   Amps
Field Current   Amps
Field Voltage   Volts

The above Form parts of the MCC hence enumerated



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