This article is about Form Wound Squirrel Cage Induction Motor Material Technical Specification of MV Motor for commercial buildings, plants and refinery projects as per international codes and standards.
Why squirrel cage is used in induction motor?
Form Wound Squirrel Cage Induction Motor Material Technical Specification
| QC Before Installation- Motors shall conform to all applicable requirements, Data sheet, Standards, and Specifications prior to release to be used as part of work. |
| Incoming motors shall be visually inspected for damage / defects occurred during transportation. |
| Motors shall be new and unused. |
| Motors shall be in accordance with the approved project-specific design drawings, diagrams, schedules, lists, databases, and associated design documents. |
| Motors exposed to ambient temperatures shall be rated in accordance with NEMA MG 1 as modified by this standard, 17-SAMSS-502, 17-SAMSS-503, 17-SAMSS-510, 17-SAMSS-518, or 17-SAMSS-520, as applicable, for a 50 deg C ambient. Motors shall be applied and sized based on their 1.0 service factor rating. |
| Motors shall be selected in accordance with Table 1. (See Attachment-1) |
| Data for motor over 100 HP shall include the following: Horsepower rating; Nameplate voltage; Full load current; Locked rotor current; Acceleration time; Permitted stall time at 80%,90%,100%and 110% rated voltage; Thermal capability curves; Number of starts allowed, from cold in first hour and subsequent hours; After a running trip, starts allowed in first hour and subsequent hours. If acceleration time exceeds permitted stall time, data on speed switch and times shall be provided; RTD data. |
| New form wound induction motor installations shall meet the vibration requirements of 17-SAMSS-502 and 17-SAMSS-520 when coupled to the driven equipment and run loaded. |
| Stator temperature monitoring for Form-Wound Motors: Resistance temperature detectors (RTD) provided for monitoring stator temperature shall be 100-ohm, platinum, three lead type with a temperature coefficient of resistance equal to 0.00385 ohm/ohm/ºC. |
| RTD’s shall be monitored by the multipurpose motor protection package which shall be set to trip or alarm on high temperature in accordance with the direction of the facility proponent. Where more than one RTD per phase is installed, the RTD that shows the highest reading during normal operating condition shall be used to provide temperature information for trip and alarm functions. |
| Commentary Note 9.2.2: Automatic trip on high stator temperature is recommended only for motors in unmanned facilities. Alarm and trip settings should be based on the reading of the highest RTD and should be in accordance with the motor manufacturer’s recommendations, if available. If manufacturer’s recommendations are not available the following guidelines may be used: For alarm only installations High Temperature Alarm, 125ºC and High Temperature Alarm, 140ºC. For alarm and trip installations High Temperature alarm, 125ºC, and High Temperature Trip, 140ºC. |
RTD’s shall be installed in accordance with Table 2.
| Bearing Temperature Monitoring for Form-Wound Motors: Horizontal motors rated 370 KW (500 HP) and above shall have bearing temperature monitoring. |
| RTD’s for bearing temperature monitoring shall meet requirements of Sec. 9.2.1 |
| Bearing temperature sensor installations shall meet the requirements of 34-SAMSS-625. |
| Bearing temperature sensors shall be monitored either by the multifunction motor protection package or by a separate integrated system protecting the motor and the driven equipment. |
| Commentary Note 9.3: Automatic trip on high bearing temperature is recommended. Settings should be in accordance with motor manufacturer’s recommendations, if available, or 90ºC for alarm and 95ºC for trip. |
As a minimum, the data listed below shall be clearly stamped on the motor’s nameplate (s):
a) Vendor’s name
b) Serial number
c) Horsepower, kVA or kW
d) Voltages
e) Phase
f) Full load power factor and efficiency
g) Frequency, in hertz
h) For antifriction bearings, the manufacturer and model number
i) For bearings with an external oil supply, the oil flow rate, in gallons per min. and the oil pressure required, in pounds/square in. gauge
j) Full-load current (amps)
k) Locked rotor amperes (LRA)
l) Full load speed, in revolutions per minute
m) Time rating
n) Temperature rise, in degrees Celsius; the maximum ambient or cooling-air temperature for which the machine was designed; and the insulation system’s designation. API Std. 541 Sec. 2.4.11.2
o) Service factor
p) Start limitations
q) Location of the magnetic center
r) Enclosure type
s) Total motor weight and rotor weight
t) Year of manufacturer
u) The frequency range for ASD driven units.
v) Type of torque/speed characteristics for which the motor is designed e.g. VT (variable torque) or CT ( constant torque)
w) Type of inverter for which the motor is intended to be used
API Std. 541-2003 Sec.2.4.11.2
| The arrangement of the equipment, including terminal housings, conduit, piping, and auxiliaries, shall be developed jointly by the purchaser and the vendor. The arrangement shall provide adequate clearance areas and safe access for operation and maintenance. API Std. 541 Sec. 2.1.5 |
| The machine and all its auxiliary devices shall be suitable for and in accordance with the area of classification system specified by the purchaser on the data sheets. Auxiliary devices shall be listed or certified where required in accordance with the area classification system specified in NFPA 70 (NEC) Article 500, 501, 502 and 505 (Class, Group, Division or Zone, and Temperature Code), or IEC 60079-10 (Zone, Class, Group, and Temperature Code), and specified local codes. API Std. 541 Sec. 2.1.7 |
| Enclosure parts shall be made of cast or nodular iron, cast steel, or steel plate. API Std. 541 Sec. 2.4.1.1 |
| The frame and mounting plates shall be of cast or nodular iron, cast steel, or welded steel plate construction, with removable end brackets or end plates to permit removal of the rotor and facilitate replacement of stator coils. API Std. 541 Sec. 2.4.2.1 |
| Only totally enclosed motors shall be provided. Totally enclosed water/air cooled (TEWAC) motors shall not be provided. |
| If auxiliary cooling fans are used for TEAAC motors, the main motors shall meet the following requirements: 1) Auxiliary cooling fan motors shall meet the requirements of 17-SAMSS-503. 2) More than one fan shall be used. Fan motors shall be easily accessible for maintenance and it shall be possible to remove and replace cooling fan motors with the main motor operating the driven equipment. 3) For motors 6000 KW (8000 HP) of greater, the heat exchanger design shall be such that the main motor meets all load and temperature rise requirements with any one auxiliary cooling fns out of service. |
| Heat air-to-air exchangers for TEAAC motors shall be designed with a minimum of 5% allowance for plugging or fouling. |
| A sole plate or base plate shall be provided. Unless otherwise specified, requirements for the motor mounting plate shall be as specified by the vendor with unit responsibility. Motor mounting plate arrangement shall be such that the complete motor assembly can be removed intact for repair without having to remove grout for motor removal or reinstall grout when the motor is returned. |
| Unless otherwise specified, minimum quantities of special mechanism for lifting, when required, shall be one per purchase order. |
| For motors 2000 KW (2700 HP) and above which operate at or above 1800 RPM, the vendor shall provide a damped unbalanced response analysis for each speed from zero to 115% of the maximum operating speed. |
| Hydrodynamic radial bearings shall be provided on horizontal motors. |
| Unless otherwise specified, the motor half coupling shall be mounted on the motor shaft with a cylindrical fit. |
| Only metallic fans are acceptable. |
| Nameplates and rotation arrows shall be of AISI 316 stainless steel with 2mm minimum thickness, securely fastened by pins of similar material, and attached at readily visible locations. API Std. 541-2003, Sec. 2.4.11.1 |
| Nameplates shall be in the English language. |
| The following additional information shall be provided on either the same nameplate or on a separate nameplate: a) Saudi Aramco purchase order number or contract number. b) Location of manufacture c) Manufacturer’s order reference number d) For explosion proof motors: Class and Group of hazardous area motor is certified or listed for and agency providing the certification. |
| Each major component of the motor shall be identified with the serial number, which may be stamped on a nameplate affixed to the component or stamped directly on the component itself. The instruction manual shall indicate where these markings can be found. The following major components shall be identified: a) Stator frame b) Stator core pack (if removable) c) Rotor d) Bearing pedestals e) Bearing end caps |
| Terminal boxes for accessory leads shall be located on the side of the motor opposite the main terminal box, unless otherwise specified. Accessory leads shall terminate on terminal blocks. Terminal boxes for accessory leads shall meet the requirement for NEMA 4 or, in the case of severe corrosive area, NEMA 4X. |
| If vertical gasketed surfaces are not provided with a drip shield, then the enclosure shall be NEMA 4X type. |
| If a terminal box contains accessories (e.g., current transformers, surge arresters, etc.), space heaters shall be provided. |
| Drains shall be provided for outdoor fabricated boxes. |
| Breathers shall be provided for outdoor fabricated boxes. |
| Removable links shall be provided. |
| Ground bus shall be provided for motors 750 KW (1000 HP) and above. |
| If differential current transformers are specified, secondary leads shall be provided. |
| All motor accessory wiring external to the machine shall be mechanically protected in galvanized rigid steel conduit terminated by stainless steel flexible liquid-tight conduit as per section 5.5 of API STD 670. Rigid steel conduit fittings shall be cast iron or cast steel. For motors specified for use in severe corrosion areas, the conduit and conduit fittings shall be either PVC coated or in stainless steel. |
| Embedded RTDs for the stator windings shall be provided as follows: Size Motor RTDs Per Phase 185 KW (250 HP) through 7500 KW (10,000 HP) 2 Above 7500 KW (10,000 HP) 3 |
| RTDs shall be 100-ohm, platinum, three-lead resistance temperature detector with a temperature coefficient of resistance equal to 0.00385 ohm/ohm/ºC from 0ºC to 100ºC. |
| Leads of sensing elements shall not be grounded in the terminal box. |
| Space heaters shall be supplied for all motors. |
| Motors rated 13.2 KV and above shall be furnished with surge capacitors and surge arresters. Unless otherwise specified, surge capacitors and arresters are not required on lower voltage motors. |
| Motors 3750 KW (5000 HP) and larger shall have provisions for self-balancing differential relay protection. Motor vendor shall provide and install 50:5 ratio, ANSI rating C20, current transformers in each phase for this purpose. |
| Horizontal motors rated in excess of 750 kW (1,000 HP) and equipped with hydrodynamic radial bearings shall be provided with two noncontacting vibration probes in each radial bearing housing and one event per revolution (key phasor) probe. If motors equipped with hydrodynamic radial and hydrodynamic thrust bearings shall be provided with two non-contacting vibration probes in each radial bearing housing, two axial position probes and one event per revolution (key phasor) probe. |
| Instruction Manuals As built vendor data sheets and all curves (thermal curves, speed-torque curves, etc.) and drawings referred to on the vendor data sheets shall be included in the operations and maintenance manuals. |
International Codes & Standards
| 1. SAES-P-101 Regulated Vendors List for Electrical Equipment 09 June, 2007 |
| 2. SAES-P-113 Motors and Generators 05 December, 2006 |
| 3. SAES-P-114 Power System and Equipment Protection 06 November 2006 |
| 4. 17-SAMSS-502 Form-Wound Induction Motors to 250 HP and Above 25 June, 2007 |
| 5. API Std. 541-2003 Form-wound Squirrel-Cage Induction Motors-500 HP and Larger |