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60034-1 IEC:2004 109

Item Machine or part Test voltage (r.m.s.)

7 Exciters (except as below) As for the windings to which they are connected

Exception 1: exciters of synchronous motors

(including synchronous induction motors) ifconnected to earth or disconnected from thefield windings during starting

1 000 V + twice the rated exciter voltage, with a

minimum of 1 500 V

Exception 2: separately excited field windingsof exciters (see item 4)

8 Electrically interconnected machinesand apparatus

A repet ition of the tests in items 1 to 7 above should beavoided if possible, but if a test is performed on agroup of machines and apparatus, each havingpreviously passed its withstand voltage test, the testvoltage to be applied to such an electrically connectedarrangement shall be 80 % of the lowest test voltageappropriate for any individual piece of the arrangement(Note 4)

9 Devices that are in physical contact with

windings, for example, temperature detectors,shall be tested to the machine frame.

During the withstand test on the machine, alldevices in physical contact with the windingshall be connected to the machine frame.

1 500 V

NOTE 1 For two-phase windings having one terminal in common, the voltage in the formula shall be the highestr.m.s. voltage arising between any two terminals during operation.

NOTE 2 Withstand tests on machines having graded insulation should be the subject of agreement.

NOTE 3 The voltage occurring between the terminals of the field windings, or sections thereof, under thespecified starting conditions, may be measured at any convenient reduced supply voltage, and the voltage someasured shall be increased in the ratio of the specified starting supply voltage to the test supply voltage.

NOTE 4 For windings of one or more machines connected together electrically, the voltage to be considered isthe maximum voltage that occurs in relation to earth.

9.3 Occasional excess current

9.3.1 General

The excess current capability of rotating machines is given for the purpose of co-ordinatingthese machines with control and protective devices. Tests to demonstrate these capabilitiesare not a requirement of this standard. The heating effect in the machine windings variesapproximately as the product of the time and the square of the current. A current in excess ofthe rated current will result in increased temperature. Unless otherwise agreed, it can beassumed that the machine will not be operated at the excess currents specified for more than

a few short periods during the lifetime of the machine. When an a.c. machine is to be used asboth a generator and a motor, the excess current capability should be the subject ofagreement.

NOTE For the capability of synchronous machines concerning the occasional negative-sequence component ofcurrent under fault conditions, see 7.2.3.

9.3.2 Generators

AC generators having rated outputs not exceeding 1 200 MVA shall be capable ofwithstanding a current equal to 1,5 times the rated current for not less than 30 s.

AC generators having rated outputs above 1 200 MVA shall be capable of withstanding a

current equal to 1,5 times the rated current for a period which shall be agreed, but this periodshall be not less than 15 s.