Section – Two Part – 3
Electrical Specification Motors and Starters
Part -3
MOTORS & STARTERS
1.0 GENERAL
The Contractor shall supply and install the motors and the starters under other sections when so mentioned, as shown on the Drawings and as herein specified.
Motor starting method and corresponding furnished starter shall be concordant.
2.0 RATING OF MOTORS
Motors shall be suitable for operation on 220-240 volt single phase or 380-420 volt 3-phase, 3-wire, 50 Hz system and shall be dripproof fan cooled to IEC 34-6 induction motor type unless otherwise indicated or specified. All motors shall have a service factor of 1.15.
Motors of ratings smaller than 5 HP shall be single phase and those of ratings 5 HP and larger shall be three phase, unless otherwise indicated or approved.
Motors of rating larger than five (5) horsepower and up to 50 HP shall be star-delta starting type, unless otherwise permitted or required by the Local Authorities.
Motors of rating five (5) horse power and smaller shall be direct on line starting type and those above 50 HP shall have auto transformer type starters unless otherwise specified or indicated on the drawings.
Every motor shall be of sufficient capacity to operate the driven equipment under all load and operating conditions without exceeding its rated name-plate current or power or its specified temperature limit. The horsepower ratings for motors shown on the Drawings must be considered as an indication only. For the use of motors other than that specified, the Contractor shall assume the cost of, and responsibility for satisfactorily accomplishing all changes (including engineering costs of redesign by the Engineer) in the work as indicated and specified. All derating resulting from site conditions shall be allowed for in the design.
Motor performances shall comply with the requirements of IEC 34-1.
3.0 TYPES OF MOTORS
All motors shall be of a type approved for starting characteristics and ruggedness as may be required under the actual conditions of operation.
All motors shall have class F insulation as a minimum requirement.
The motors shall be designed so that the maximum temperature rise at continuous run under full load and operation conditions shall be in accordance with IEC Standards for Motors and Generators and based on the local ambient temperature.
4.0 GENERAL DESIGN OF MOTORS
Motor windings shall be braced to withstand successfully the stresses resulting from the method of starting. The windings shall be treated thoroughly with approved insulating compound suitable for protection against moisture and slightly acid or alkaline conditions.
Bearings shall be of the self-lubricating type, designed to ensure proper alignment of rotor and shaft, and to prevent leakage of lubricant.
Bearings for open motors shall be of the sleeve or ball type, as specified under respective items of mechanical equipment.
Indoor motors located in relatively clean surrounding, free from any abrasive or conducting dust or chemical fumes, shall be enclosed ventilated dripproof type. Otherwise motors shall be totally enclosed fan cooled type.
Vertical motors if any shall be provided with thrust bearings adequate for all thrusts to which they can be subjected in operation.
Vertical motors of open type shall be provided with drip hoods of approved shape and construction. When the drip hood is too heavy to be easily removed, provision shall be made for access for testing.
5.0MOTOR TERMINAL BOXES AND LEADS
Motors shall be furnished with oversize conduit terminal boxes to provide for making and housing the connections and with flexible leads of sufficient length to extend for a distance of not less than 10 cm beyond the face of the box. The size of cable terminals and conduit terminal box holes shall be as approved by the Engineer. An approved type of solderless lug shall be supplied. Totally enclosed motors shall have cast iron terminal boxes.
6.0 MOTOR SHOP TESTS
Motor shop tests shall be made in accordance with IEC Test Code or approved equal.
Complete tests of each motor supplied shall be made and certified shop test data sheets shall be submitted, unless witness shop tests are required by the Detail Specifications pertaining to the equipment. Each motor shall be tested for efficiency and power factor at 50, 75 and 100 percent of its rated horsepower, for temperature rise, torque, starting current and dielectric strength; and for compliance with all specified performance requirements.
7.0MOTOR STARTERS
Motor Starters shall be built and sized in accordance with IEC Standard 158-1,BS 5424 and IEC 292-1&2, or approved equal. Starters shall be non-reversing, magnetic type unless otherwise indicated or specified.
All starters shall be provided with thermal cutout devices in each phase calibrated for close protection of the motors against overloads. These devices shall trip the starters in case of overload and shall not allow it to be reset except manually. The thermal overload relays shall be adjustable from 90 to 110 percent of nominal rating. A single calibration adjusts all three legs. The overload relay shall be ambient compensated.
The starter shall be provided with auxiliary contacts for the connection of signaling, interlocking and other circuits as required for the controls.
Unless otherwise indicated, all starters shall be provided with START-STOP pushbuttons, and RED and GREEN pilot lights, all located on the starter front cover. An overload reset button shall be provided inside the cover. Pushbuttons shall be momentary contact or maintained type as applicable to the function of control.
Starters shall have horsepower ratings at least equal to ratings of motors they serve.
Voltage of control circuit shall not exceed 240 volts for starters in motor control centers or panels. Individually mounted starters or combination starters may have their control voltage on 380-415 volts provided local regulations or local inspectors do not forbid the use of same. The Contractor when utilizing such voltage for control shall provide a clear warning of existence of such voltage within the station. If 240 volts are required by the local regulations or local inspectors, a neutral conductor shall be brought within the feeder of the starter of approved cross section, at no extra charge.
Starters shall be electrically held in, providing inherent undervoltage release.
Starters when not part of a motor control center and are located outdoors shall be encased in an IP 55 enclosure, unless otherwise indicated.
A. Direct on line (DOL) Starters
DOL starters for voltages up to and including 1000V a.c. shall comply with IEC 947. They shall be rated for intermittent periodic duty or intermittent duty class 0.3 and comply with the requirements of utilization category AC-3.
B. Automatic Star-Delta (ASD) Starters
In all types of star-delta starters the correct phase relationship between the star and delta connections to minimise disturbance on changeover shall be maintained. For example, if the supply phase sequence is L1, L2, L3 and the star point is S then connections shall be as follows:-
Winding 1Winding 2Winding 3
beginning/endbeginning/end beginning/end
Connection
In STARL1SL2SL3S
Connection
In DELTAL1L3L2L1L3L2
In all star-delta starters the star and delta contactors shall be electrically and mechanically interlocked so that they cannot close or be closed at the same time.
Where overload relays are connected in the phase circuit, the overload relay scales shall be clearly marked to show whether they represent line current or whether the scale must be multiplied by 1.7 to represent line current.
C. Open Transition and Closed Transition Start-Delta Starters
Automatic changeover timers shall be adjustable from one second up to at least 20 seconds but the transition from star to delta windings shall be achieved without any intentional delay. Closed transition timers shall have tamper-proof factory-set adjustment.
Closed transition star-delta starters shall be arranged for Wauchope connection. The grid resistors shall be rated for 12 seconds in any 90 seconds, for a 260 deg.C rise from a 40 deg.C ambient temperature. Cables connecting onto the grid resistors shall be heat resisting type suitable for the above temperature rise.
Resistance banks shall be housed in separate sections of the control panel or starter.
8.0 AUTO-TRANSFORMER STARTERS
Shall comply with BS EN 60947-4.1 (1992). They shall be rated for intermittent duty Class 0.3 and shall comply with the requirements of utilization category AC-3. The starters shall be arranged for 'Korndorffer' closed transition connection. The transformer shall, unless otherwise specified, have tappings of 65%, 70% and 75% of line voltage.
A. Starters for Dual-Wound and Pole-Change Motors
Shall be electrically and mechanically interlocked so that it is impossible for both high and low speed contactors to close or be closed at the same time. The parts of the composite starter shall comply with the relevant specification for individual starters. Adjustable timers shall be fitted into the control circuit so that there is a time delay between switching off the high speed contactor and switching on the low speed contactor. When high speed is selected the motor shall run in low speed for a preset time before changing to high speed.
B. Soft-Start/Stop Starters
Soft start/stop starters shall be supplied as a unit with an enclosure suitable for panel mounting.
Starters shall be rated for 380V a.c., 50 Hz supply an a temperature operating range of 0 to 50 deg.C. Noise and impulse immunity shall be to ANSI C37-90A, IEC 225-4, IEE 472 (1974) and SEN 361503.
Soft start shall be via a range of switch selectable ramp times of between 0.5 and 60 seconds with a ramp voltage which increases linearly with time.
Soft stop shall be via a range of switch selectable ramp times of between 1 to 120 seconds.
The control circuit shall incorporate a remote emergency stop facility. This function shall override the normal `soft stop' of the starter.
Filters shall be provided at the inlet and outlet of such devices.
The harmonic current spectrum of each soft-start/stop starter shall be provided by the manufacturer for the calculation and provision of suitable filtration at the electrical switchboard.
A contactor shall be provided to isolate the soft start/stop unit when the motor is not required to run. The contactor shall be arranged to switch 'off-load'.
The maximum starter current shall be 2.0 times full load.
The control panel manufacturer shall calculate the maximum heat dissipation from all soft-start devices and incorporate adequate ventilation methods to ensure that the internal temperature within the control does not exceed 40 deg.C.
C. Frequency Drives (Inverters)
Frequency inverter drives shall be of the ABB SAMI range type or alternative, approved by the Engineer.
The frequency drive shall employ pulse width modulation (PWM) using thyristor or transistor switches.
The rating of the frequency drive shall be sufficient for the continuous maximum rating of the motor and not its running load.
The frequency drive unit shall have an efficiency in excess of 90%.
Facilities shall be provided to allow the connection of an emergency Stop Push Button to ensure effective direct stopping of the drive if dangerous situations arise. The means provided shall include direct connection to an air-break, e.g. a contactor, arranged such that its opening on-load:
a) does not inhibit any in-built deceleration provided by the variable speed controller.
b) does not produce additional safety hazards
c) and does not cause damage to the controller.
Such contactors must be IEC 947 with utilisation category AC-3. The frequency drive shall be capable of switching on to a motor already rotating in either direction.
If the mains cable distance between the motor control panel (MCP) and the motor exceeds 30 meters the inverter shall be located adjacent to the motor, otherwise the inverter shall be housed within the MCP.
Inverter Technical Features:
The input to the frequency drive shall be of an uncontrolled bridge rectifier type, to limit harmonic distortion.
The speed shall be smoothly adjustable, and controlled by one of the following:
Potentiometer- manual operation
and 0-10V dc signal- auto operation
or 4-10mA signal- auto operation
Overcurrent, short-circuit and earth fault protection of the output shall be provided within the control system to comply with the IEE Regulations. Reset of any fault condition shall be manual.
The system shall provide protection against phase loss. If not included within the frequency drive, then an external phase loss detection device shall be fitted.
Full rated output shall be provided continuously with an ambient temperature of 50 deg.C. The control panels housing frequency drives shall be provided with suitably rated ventilation fan to ensure that this temperature is not exceeded.
The starting arrangement shall include a ramp speed control, to achieve starting currents not exceeding normal full load current wherever possible.
The output frequency range shall nominally be 1Hz to 50 Hz.
The frequency drives shall provide the following visual information:
-Motor Speed, Motor Overload, Motor Short Circuit, Overvoltage, Undervoltage, Equipment heating.
-The control circuits shall be immune to interference caused by operating on normal raw mains supply in an industrial environment.
-Where frequency drive systems might be a source of Radio Frequency Interference (RFI) sufficient to interfere with the proposed functioning of adjacent computer based equipment, RFI suppression at source shall be applied.
-The manufacturer shall provide details regarding the production of mains-borne interference and harmonic. Written guarantees shall be given by the manufacturer that these levels of interference and harmonics shall not be exceeded over the full operating speed of the drive.
-Where screening of cables between the frequency drive and motor is required, the type of cable recommended must be indicated at the tender stage. The recommended cable must ensure that the level of any radio interference is limited to comply with BSEN 55014:1993.
-The harmonic current spectrum of each frequency drive shall be provided by the manufacturer for the calculation and provision of suitable filtration at the electrical switchboard.
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9.0 MOTOR CIRCUIT PROTECTIVE DEVICES
Motor circuit protective devices are rated in accordance with IEE Wiring Regulations. Alternative proposals based on manufacturers recommendations shall be subject to the Engineer's Approval. The Contractor shall in any case be responsible to assure that the circuit protective devices shall carry the starting current with no tripping, and if reducing trip rating results in a reduction in frame size, the Contractor shall make sure that the new rating withstands the available short circuit current.
10.0 APPLICABLE STANDARDS
1.Specification of Contractors:BS 5424 Part 2 (1993).
2.Specification for Motor Starters:BSEN 6094 7-4-1: 1992.
3.Radio Frequency Suppression:BSEN 55014:1993.
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