GB/T 20140-2016Measurement method and evaluation criteria of dynamic characteristic and vibration on stator end windings of cylindrical synchronous generators (English PDF)

4.1.2 Measured parameters

The measured parameters are as follows:

a) natural frequency of phase connection and main connection of stator end windings, in Hz;

b) elliptical or 4-lobe mode shape of integral stator end windings;

c) response ratio value corresponding to natural frequency of frequency response function of stator end windings and connection original point, in (m/s

2

)/N.

4.1.3 Measuring environment

Modal test analysis for stator end windings shall be carried out at room temperature.

4.1.4 Measuring position and requirement

The measuring points for connection natural frequency test are mainly located on the axial and tangential line of phase connection and main connection of exciter end windings (radial natural frequency can also be measured). For some units, when exciter end phase connection and end are connected tightly, becoming an entirety which is hard to differentiate, the measurement of natural frequency of connection can be omitted. The manufacturer usually only measure phase connection; the manufacturer measures main connection during type test; the power plant can measure natural frequency of main connection.

The measuring positions for integral end mode shape test are located on the cross sections of end windings on the steam side and exciter side. Take three circles respectively as shown in Figure 1; distribute the measuring points evenly along the circles, with at least 16 measuring points for 2-pole generators and at least 32 measuring points for 4-pole generators. It is recommended that the measurement shall be carried out in the order from circle 1 to circle 3 (see Figure 1). Usually, the data of circle 2 and circle 3 can be measured as required by the analysis, when the mode of circle 1 is measured.

Use viscous material or other methods to fix acceleration sensor temporarily on corresponding measuring positions.

parameters of generator: rotational speed, stator voltage, stator current, active power and reactive power.

4.2.2 Measured parameters

Absolute vibration displacement amplitudes of stator end windings, mainly including peak to peak values of pass frequency (frequency range greater than or equal to rotational frequency) and double frequency vibration displacement, expressed in µm.

4.2.3 Measuring conditions

The measuring conditions are as follows:

a) generators’ rated idling;

b) generators’ rated no-load;

c) generators’ rated short circuit;

d) generators’ rated load (on site).

4.2.4 Arrangement of measuring points and mounting

Arrange measuring points on stator windings nose joint, stator windings outgoing line and stator end windings fastener or arrange measuring points at other positions of winding bar as required. Arrange measuring points at the positions having significant abrasion or vibration in accordance with the modal test results of stator end windings.

Sensor and signal line shall be mounted securely without influencing the operation and overhaul of generators. When they are used on hydrogen cooling generators, signal line shall be led out of generator stand, which shall meet the requirements for air tight test for generators.

5.1 Measuring apparatus for dynamic characteristic

5.1.1 Force hammer

Force hammer shall be equipped with a force sensor. The hammer body shall have sufficient mass in order to excite stator end windings. Force hammer of body weight about 1.4 kg is recommended; hammer cover shall be made of materials such as rubber or soft plastic.

5.1.2 Acceleration sensor

Use piezoelectric type acceleration sensor to measure vibration response. ICP type acceleration sensor and signal acquisition and analysis equipment directly matched and connected with it are recommended. The acceleration sensor having a sensibility

6.2 Evaluation criteria of vibration on stator end windings of cylindrical synchronous

generators

6.2.1 During the rated no-load or rated short-circuit operation of generators, the peak

to peak values of pass frequency (frequency range greater or equal to rotational frequency) and double frequency vibration displacement are less than 100 µm.

6.2.2

During the normal operation of generators, if the peak to peak value of pass frequency (frequency range greater or equal to rotational frequency) and double frequency vibration displacement of stator end windings are less than 250 µm, it is generally acknowledged that they are suitable for long-term operation without limit.

6.2.3

During the normal operation of generators, if the peak to peak values of pass frequency (frequency range greater or equal to rotational frequency) and double frequency vibration displacement of stator end windings are greater than 250 µm and less than 400 µm, an alarm signal shall be given. Generally, the units can continue to operate for a certain time under such circumstances; during such periods, the reasons for the vibration shall be found out by research and it shall be observed whether vibration can be stabilized within a certain range.

6.2.4

During the normal operation of generators, if the peak to peak values of pass frequency (frequency range greater or equal to rotational frequency) and double frequency vibration displacement of stator end windings are greater than 400 µm, a halt signal shall be given. Generally, it is inappropriate to continue operation under such circumstances; stop the machine as soon as possible for inspection and treatment, or take corresponding measures to lower the vibration to below the limits in accordance with actual conditions.

6.2.5

During the normal operation of generators, if the variation of the peak to peak values of pass frequency (frequency range greater or equal to rotational frequency) and double frequency vibration displacement of stator end windings is greater than

100 µm, an alarm signal shall be given and the monitoring shall be enhanced.

Generally, if the variation of vibration amplitude reaches a certain quantity, the reasons for the variation shall be found out, no matter whether the vibration amplitude increases or decreases. Such variation can be instantaneous or developed along with time; it may indicate that a damage has occurred, or a fault is to occur, or some abnormal conditions exist.