Bsi bs en 60034 4 1995 scan

Determination of Potier reactance from the no-load and sustained three-phase short-circuit characteristics and the excitation current corresponding to the rated voltage and rated arma- t

scope

This standard applies to three-phase synchronous machines of 1 kVA rating and larger with rated frequency of not more than 400 Hz and not less than 15 Hz

The test methods are not designed for special synchronous machines, including permanent magnet field machines and inductor type machines While these tests generally apply to brushless machines, specific variations exist, necessitating caution during their application.

Object

The object of this standard is to establish methods for determining characteristic quantities of three-phase synchronous machines from tests

This standard does not mandate the execution of all tests outlined for any specific machine; instead, the selection of tests to be performed will be determined through a special agreement.

Tests for determining synchronous machine quantities should be conducted on a completely sound machine, all the devices for automatic regulation being switched off

Unless otherwise stated, the tests are conducted at the rated speed of rotation

Measuring instruments and their accessories, including measuring transformers, shunts, and bridges, should generally have an accuracy class of no more than 1.0, as specified in IEC Publication 51 for direct acting indicating analogue electrical measuring instruments For the determination of direct current (d.c.) resistances, the required accuracy class should be no greater than 0.5.

At this stage, the accuracy class for the oscillographic measuring equipment is not specified However, it is essential to select an appropriate class based on the rated frequency of the machine being tested, ensuring that readings are obtained within the linear range of the vibrator's amplitude versus frequency characteristic.

The measurement of the speed of rotation, of synchronous machines may be conducted by means of a stroboscopic method or by using tachometers (mechanical or electrical)

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When a machine operates synchronously with another machine or independently, it is acceptable to measure its frequency using a frequency meter instead of measuring the speed of rotation.

During tests, the temperature of the windings is measured when it influences the quantities being determined or when it is necessary for ensuring the machine's safety.

To ensure safety during testing, it is advisable to begin tests only after the machine has operated at no-load with standard cooling or has rested sufficiently to achieve a low starting temperature Additionally, temperatures should be closely monitored or pre-determined to allow for the test to be halted before reaching excessive levels.

During the test, the machine winding connection, as a rule, should be as for normal working

The calculation of all quantities is based on the assumption of a star connection for the armature winding, unless specified otherwise, such as in the case of a delta connection If the armature winding is connected in delta, the values derived from this standard will reflect those of an equivalent star-connected winding.

All quantities and characteristics should be expressed in per unit values based on the rated voltage (U) and apparent power (S) as the fundamental references Consequently, the basic current and basic impedance can be determined accordingly.

For convenience, intermediate calculations can be conducted using physical values before converting them to per unit values, with time expressed in seconds When calculating characteristics and creating diagrams, the excitation current corresponding to the rated voltage on the no-load curve should be used as the reference value for excitation current.

If a machine has several rated values, those taken for the basic values should be stated

The system referenced above is accepted in this standard, with small letters representing quantities in per unit values and capital letters indicating physical quantities.

In the formulae given in this standard for determining synchronous machine reactances the positive sequence armaturc resistance, unless otherwise stated, is considered to be negligible

When the positive sequence armature resistance constitutes more than 0.2 of the measured reactance the formulae must be considered as approximate

This standard provides definitions for various quantities and their experimental determination methods, aligning with the widely accepted two-axis theory of synchronous machines It represents all circuits, including the field winding and stationary circuits, using two equivalent circuits: one along the direct axis and the other along the quadrature axis The approach either neglects armature resistance or considers it only approximately.

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This standard for studying transient phenomena incorporates three reactances—synchronous, transient, and sub-transient—along the direct axis, along with two time constants: transient and sub-transient Additionally, it considers two reactances—synchronous and sub-transient—along the quadrature axis, and includes the armature short-circuit time constant.

The time constants are derived from the assumption of an exponential decrease in components such as currents and voltages In cases where the measured component, like that of a solid rotor machine, does not exhibit a pure exponential decay, the time constant should be understood as the duration needed for the component to reduce to approximately 36.8% of its initial value Consequently, the exponential decay curves associated with these time constants should be viewed as equivalent representations of the actual measured data.

3.7 Synchronous machine quantities vary with saturation of the magnetic circuits In practical calculations both saturated and unsaturated values are used

In this standard, the "saturated value" of reactances and resistances is defined as the rated armature voltage, while the "unsaturated value" corresponds to the rated armature current, with the exception of synchronous reactance, which is not classified as saturated.

The rated armature voltage reflects the magnetic state of the machine during a sudden short circuit of the armature winding while operating at no-load rated voltage and rated speed.

Direct-axis synchronous reactance A', 5 Short-circuit ratio KE 6 Quadrature-axis synchronous reactance X, 7 Direct-axis transient reactance XA

The ratio of the sustained value of the fundamental alternating current (a.c.) component of armature voltage, generated by the total direct-axis armature flux from direct-axis armature current, to the fundamental a.c component of this current, is observed when the machine operates at its rated speed.

The direct-axis synchronous reactance $X$ in its unsaturated state is established based on the no-load saturation characteristics and the sustained three-phase short circuit characteristics, as outlined in Clause 27 and Sub-clauses 25.1 and 26.1, respectively.

The ratio of field current at rated armature voltage during open-circuit conditions to the field current at rated armature current under sustained symmetrical short circuit conditions is measured while the machine operates at rated speed.

5.1 The short-circuit ratio is determined (see Sub-clause 27.1) from the no-load saturation (see Sub- clause 25.1) and sustained three-phase shon circuit (see Sub-clause 26.1) characteristics

The ratio of the sustained value of the fundamental alternating current (a.c.) component of armature voltage, generated by the total quadrature-axis armature flux from the quadrature axis armature current, to the fundamental a.c component of this current, is observed when the machine operates at its rated speed.

Quadrature-axis synchronous reactance can be determined through several methods: negative excitation, as outlined in Clauses 34 and 35; low slip measurements discussed in Clauses 36 and 37; and on-load measurement of the load angle, detailed in Clauses 38 and 39.

The first two methods are preferred

The ratio of the initial change in the fundamental alternating current (a.c.) component of armature voltage, caused by the total direct-axis armature flux, to the simultaneous change in the fundamental a.c component of direct-axis armature current is analyzed This occurs while the machine operates at rated speed, excluding the high decrement components during the initial cycles.

Direct-axis transient reactance can be determined through several methods, including sudden three-phase short circuit tests, voltage recovery assessments, and calculations based on test values of specific parameters.

7.1 the formula given in Clause 72

The method of the sudden three-phase short circuit is preferred It permits saturated and unsaturated values of A'; to be determined.

Direct-axis subtransient reactance X i 9 Quadrature-axis subtransient reactance Xi 11 Negative-sequence resistance R2 12 Zero-sequence reactance A',

The ratio of the initial value of a sudden change in the fundamental alternating current (a.c.) component of armature voltage, caused by the total direct-axis armature flux, to the simultaneous change in the fundamental a.c component of direct-axis armature current, occurs while the machine operates at its rated speed.

Direct-axis subtransient reactance can be determined through several methods: a) sudden three-phase short circuit (refer to Clause 40 and Sub-clause 41.1); b) voltage recovery (see Clause 42 and Sub-clause 43.1); c) applied voltage with the rotor positioned along the direct and quadrature axes relative to the armature winding field axis (consult Clauses 44 and 45); and d) applied voltage with the pole axis in an arbitrary position (see Clauses 46 and 47).

Thc sudden three-phase short circuit method is preferred It permits saturated and unsaturated values of ,Yi to be determined

The applied-voltage methods (c and d) are suitable for determining the unsaturated value of g; however, they are generally impractical for the saturated value due to the high current demands and the risk of overheating solid components.

9 Quadrature-axis subtransient reactance Xi

The ratio of the initial change in the fundamental alternating current (a.c.) component of armature voltage, caused by the total quadrature-axis armature flux, to the simultaneous change in the fundamental a.c component of quadrature-axis armature current, occurs while the machine operates at its rated speed.

STD.BSI B S EN b003q-4-ENGL 1995 1 b 2 4 b b 9 üôb75ii3 T b 3

The quadrature axis subtransient reactance can be determined using two methods: first, by applying voltage while positioning the rotor along the direct and quadrature axes relative to the armature winding field axis; and second, by applying voltage with the pole axis set in any arbitrary position.

Both methods are effectively interchangeable for determining the unsaturated value However, they are generally impractical for assessing the saturated value due to the high current demands and the risk of overheating solid components.

The ratio of the reactive fundamental component of negative-sequence armature voltage to the sinusoidal negative-sequence armature current at rated frequency is analyzed, with the machine operating at its rated speed.

A different reactance value may be obtained when using a current that includes harmonics, but the accurate value of 4 is determined with sinusoidal current.

The ratio of the in-phase fundamental component of negative-sequence armature voltage to the sinusoidal negative-sequence armature current at rated frequency is crucial for understanding machine performance at rated speed.

Note - A different value might be obtained for this mistancc if the fundamental component of a current which also contains harmonics, is u d

Negative-sequence reactance and resistance can be determined through several methods: a) conducting a line-to-line sustained short circuit test, as outlined in Clauses 48 and 49 and Sub-clause 49 I; b) analyzing negative-phase sequence data, referenced in Clauses 50 and 51; and c) calculating negative-sequence reactance from the test values of X.

(see Clause 8) and Xi (see Clause 9); the calculation is made using the equation given in Sub- clause 72.1

The line-to-line sustained short-circuit method is preferred

The quotient of the reactive fundamental component of zero-sequence armature voltage, caused by the fundamental zero-sequence armature current at rated frequency, is analyzed while the machine operates at rated speed.

The ratio of the in-phase fundamental component of zero-sequence armature voltage to the corresponding fundamental zero-sequence armature current at rated frequency is observed when the machine operates at its rated speed.

Zero-sequence reactance and resistance can be determined using two methods: applying single-phase voltage to three phases connected in series (open delta) or conducting a sustained short-circuit from line-to-line and to neutral.

parallel (see Clauses 52 and 53); clause 55.1)

The method of single-phase voltage application to the three phases connected in series is preferred.

Potier reactance A',,

The Potier method utilizes an equivalent reactance instead of the armature leakage reactance to determine the excitation under load This approach considers the extra leakage from the field winding during load conditions and in the overexcited region, resulting in a value that exceeds the actual armature leakage reactance.

The Potier reactance is determined in accordance with Clause 30

1 S Armature and excitation winding direct-current resistance Ra and Rf

Direct-current winding resistance is determined by the following methods: a) voltmeter and ammeter (see Clauses 56 and 57); b) single and double bridge (see Clause 56 and Sub-clause 57.1)

The single bridge method is not permissible for measuring resistances less than 1 a

16 Positive-sequence armature winding resistance R i

The ratio of the in-phase component of the positive sequence armature voltage, which accounts for direct-load losses in the armature winding and stray load losses in conductors, is influenced by the sinusoidal positive sequence armature current while the machine operates at its rated speed.

16 I The positive-sequence armature winding resistance is determined in accordance with Sub- clause 72.2

17 Direct-axis transient open-circuit time constant T &

The time needed for the slowly changing component of the open-circuit armature voltage, influenced by the direct-axis flux, to drop to approximately 36.8% of its initial value after a sudden change in operating conditions is measured while the machine operates at its rated speed.

The direct-axis transient open-circuit time constant is determined by the following methods: u) field current decay with open-circuit armature winding (see Clauses 58 and 59);

17.1 h) voltage recovery (see Clause 42 and Sub-clause 43.2); c) calculation from the test values of X, (see Clause 4), Xi (see Clause 7) and T; (see Clause 18) by the formula given in Clause 72

The field current decay method is preferred

18 Direct-axis transient short-circuit time constant s i current following a sudden change in operating conditions to decrease to 1/& value the machine running at rated speed

The direct-axis transient short circuit time constant is determined by the following methods:

Thc time required for the slowly changing component of direct-axis short-circuit armature

18 I al sudden three-phase short circuit (see Clause 40 and Sub-clause 41.2);

BS 4999: Part 104: 1988 outlines the procedures for measuring field current decay with the armature winding short-circuited, as detailed in Clauses 60 and 61 Additionally, it provides a method for calculating the values of \$X_d\$ (Clause 4), \$X_i\$ (Clause 7), and \$r_{io}\$ (Clause 17) using the formula specified in Clause 72.

For determining the internal reactance (\$X_i\$) through a sudden short-circuit test, it is essential to also measure the resistance (\$r_i\$) during the same test In contrast, in other scenarios, the preferred method is to utilize the field current decay approach while the armature winding is short-circuited.

19 Direct-axis subtransient short-circuit time constant T:

The time needed for the rapidly changing component in the direct-axis short-circuit armature current to reduce to approximately 0.368 of its initial value, after a sudden change in operating conditions, is observed during the first few cycles while the machine operates at rated speed.

19.1 The direct-axis subtransient short-circuit time constant is determined by the sudden three-phase short-circuit method (see Clause 40 and Sub-clause 41.3)

20 Armature short-circuit time constant T,

The time needed for the aperiodic direct current component in the short-circuit armature current to reduce to approximately 0.368 of its initial value, after a sudden change in operating conditions, is measured while the machine operates at its rated speed.

The armature short-circuit time constant is assessed through a sudden three-phase short-circuit test using two methods: a) observing the reduction of the periodic (a.c.) component in the excitation winding current, and b) measuring the decrease of the aperiodic (d.c.) components in the armature winding phases.

(see clause 40 and Sub-clause 41.5); c) calculation from the test values of Xz (see Clause 10) and Ra (see Clause 15) by the formula given in Sub-clause 72.3

The method of measurement of the decrease of periodic component in the excitation winding current is preferred

The time needed to accelerate the rotating components of a synchronous machine from a standstill to its rated speed is determined by a constant accelerating torque This torque is calculated as the ratio of the rated active power output to the rated angular velocity.

Nores 1 - For synchronous condensers, the rated active power (output) is r e p i a d by the ntcd apparent powcr

When determining the acceleration time for a group of mechanically coupled machines, the torque is calculated based on the rated active power and the rated angular velocity of the base synchronous machine.

The quotient of the kinetic energy stored in the rotor when running at rated speed and of the rated apparent power

22.1 The acceleration time of a machine or group of machines and the stored energy constant are determined by the following methods: u) suspended rotor oscillation (see Clauses 62 and 63);

The article discusses various operational aspects of machinery, including the auxiliary pendulum swing, no-load retardation, on-load retardation while functioning as a motor, and acceleration following sudden unloading when operating as a generator.

All the above-mentioned methods are practically equivalent The application of one or another method depends on the design and the apparent power of the machine under test

Rated excitation current Ifn power-factor and speed

The rated excitation current can be determined through direct measurement during operation under rated conditions or graphically using methods such as Potier’s vector diagram, the ASA diagram, or the Swedish diagram.

The method of direct measurement is preferred, but the graphical methods are practically

The current in the excitation winding when the machine operates at rated voltage, current, equivalent to it

The rated voltage regulation in an alternator is determined with the armature open-circuited, maintaining constant speed and excitation current This can be assessed through direct measurement or graphically using the no-load characteristic, as outlined in Sub-clause 25.1, along with the rated excitation current.

The change in the terminal voltage when rated operation is replaced by no-load operation with The rated voltage regulation is determined by the following methods:

(see Clause 23 and Sub-clause 23.1) obtained from tests

SECTION FOUR - DESCRIPTION OF THE TESTS AND DETERMINATION

OF MACHINES QUANTITIES FROM THESE TESTS

The no-load saturation test is performed by operating the machine as a generator using a prime mover, running it as a motor without any shaft load from a symmetrical three-phase voltage source, and during the machine's retardation phase.

In the no-load saturation test, it is essential to simultaneously measure the excitation current, line voltage, and frequency (or speed) The excitation should be adjusted gradually from high to low voltage, with evenly distributed points, ideally starting from the voltage corresponding to the excitation at rated load, but not dropping below 1.3 times the rated voltage of the machine under test, down to 0.2 times its rated voltage, unless the residual voltage exceeds this value.

When the excitation current is decreased to zero, the residual voltage of the generator is measured

Tiêu đề	Rotating Electrical Machines Part 4 Methods For Determining Synchronous Machine Quantities From Tests
Trường học	British Standards Institution
Chuyên ngành	Electrical Engineering
Thể loại	Standard
Năm xuất bản	1995
Thành phố	London

Định dạng
Số trang	53
Dung lượng	2,38 MB