IEEE 620-1996 pdf download IEEE Guide for the Presentaton of Thermal Limit Curves for Squirrel Cage Inducton Machines
1.Overview
1.1 Scope
This guide applies to three-phase squirrel cage induction machines. 250 hp (200 kW) and above and designedfor specified load and application conditions. This guide provides a consistent way to show how the thermalimit curves for squirrel cage induction machines are to be presented.
1.2 Word usage
The word shall indicates andatory requirements strictly to be followed in order to conform to the standardand from which no deviation is permitted (shal! equals is required to)…7
The word should indicates that among several possibilities one is recommended as particularly suitablewithout mentioning or excluding others: or that a certain course of action is preferred but not necessarilyrequired (should equals is recommended thaf).
The word may is used to indicate a course of action permissible within the limits of the standard (may equalsis permitted to).
The word can is used for statements of possibility and capability, whether material. physical, or causal (canequals is able fo).
2.Normative references
The following referenced documents are indispensable for the application of this document (i.e., they mustbe understood and used, so each referenced document is cited in text and its relationship to this document isexplained).For dated references, only the edition cited applies. For undated references, the latest edition of thereferenced document (including any amendments or corrigenda) applies
There are no normative references in this standard
3.Thermal Overloads
3.1 General
A thermal overload is a condition when a machine experiences higher temperatures than the limitsrecommended by the manufacturer, This can occur during a transient event such as starting of the machine orduring continuous oneration above its nameplate rating, Although thermal overloads tvpically do not causeimmediate failure, they can result in reduced operating life by creating damaging mechanical stresses orincreased thermal aging of insulation, This standard defines the methods by which manufacturers specifthermal limits, so the users can establish best operating practices and/or install suitable protective devices tokeep the duration of thermal overloads to a minimum.
3.2 Causes
Thermal limit in this standard refers to the condition in which the stator and/or rotor cage windings ofa squirelcage induction machine exceeds the specified temperature limits by the manufacturer. There are many reasonsfor over temperature; some of the most common reasons are as follows:
aThe machine may lock up, i.e., remain at zero speed with voltage applied to the stator winding, asmight happen in the case of low starting voltage and/or mechanical malfunction.
6The machine may start but fail to accelerate to its running speed, due to inadequate accelerating torqueat some speed lower than the breakdown torque point, causing it to run at hat sub-synchronous speed.
The machine may be overloaded continuously at close to its operating speed. The machine will havegdifferent thermal limits based on the cooling system of the machine.
Under the locked-rotor condition, there is normally no ventilation, and the heat loss from the windings is byconduction and radiation. During acceleration, depending on the speed, the heat loss is both by conduction andby the ventilating effect of air movement. During running overloads, the normal ventilation of the machine isthe primary mode of cooling.
IEEE 620-1996 pdf download
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