GB/T 20834-2024Technical requirements for motor-generator (English PDF)

4 Site operating conditions

Unless otherwise specified, the motor-generator shall be capable of continuous operation at its rating under the following ambient conditions: altitude not exceeding 1 000 m; cooling air temperature not exceeding 40 °C; inlet water temperature of the air coolers and oil coolers not higher than 30 °C and not lower than 5 °C; relative humidity not exceeding 85 %.

The machine shall also meet the seismic acceleration requirements of the site. The purchaser shall provide the required horizontal and vertical acceleration values on the basis of the geographical conditions of the site.

For operating environments differing from the above, the site operating conditions are to be agreed between supplier and purchaser.

5 Ratings and parameters

5.1 The rated capacity in generating operation is the apparent power delivered at rated frequency, rated voltage and rated power factor, expressed in MVA. The rated power in motoring operation is the mechanical power delivered at the shaft at rated frequency, rated voltage and rated power factor, expressed in MW. The capacity and power of the motor-generator shall match the turbine-mode output power and the maximum pump-mode input power of the pump-turbine.

5.2 The rated voltage of the motor-generator should be selected from the following voltage levels, in kV: 6.3, 10.5, 13.8, 15.75, 18, 20 and 22.

5.3 In generating operation the rated power factor should be not lower than 0.875 (overexcited) for a rated capacity not greater than 150 MVA, not lower than 0.9 (overexcited) for a rated capacity greater than 150 MVA and not greater than 350 MVA, and not lower than 0.925 (overexcited) for a rated capacity greater than 350 MVA. In motoring operation the rated power factor should be not lower than 0.975 (overexcited).

5.4 The rated rotational speed is selected in accordance with GB/T 7894.

5.5 The range of steady-state voltage and frequency variation is divided into two zones, A and B, shown in Figure 1; the extent of zone A may be adjusted by technical agreement between supplier and purchaser. Other requirements for voltage and frequency variation during operation follow GB/T 7894. The motor-generator shall meet the requirement for a frequency variation from 0 Hz to 52.5 Hz when starting in motoring operation.

5.6 The weighted average efficiency is calculated by the formula given in GB/T 7894-2023, the purchaser supplying the weighting coefficients for generating and motoring operation according to how the unit is operated in the system. Losses and efficiency should be determined by the calorimetric method in accordance with GB/T 25442 and GB/T 5321. The losses to be included are: copper losses of the stator winding; copper losses of the field winding; core losses; windage losses; guide bearing losses; thrust bearing losses, counting only the share attributed to the rotating parts of the motor-generator; stray losses; excitation system losses, such as those of the excitation transformer, rectifier and voltage regulator; brush electrical and friction losses; and other losses, such as those associated with the external circulating oil pump of the thrust bearing and with added cooling fans.

5.7 Base values for electrical parameters such as synchronous reactance, transient reactance, subtransient reactance, short-circuit ratio and the time constants shall refer to generating operation, and the parameters and time constants shall satisfy GB/T 7894.

5.8 With the stator winding on open circuit, at no-load rated voltage and rated speed, the total harmonic distortion of the line voltage waveform shall not exceed 3 %.

6 Temperature

6.1 Under the ambient conditions of Clause 4 and at the rated duty, the machine shall be capable of long-term continuous operation and the temperature rise of the stator winding, field winding, stator core and other parts shall not exceed the limits of Table 1. Table 1 gives limits in kelvin for three measuring methods, the infrared method, the resistance method and the embedded temperature detector method: 100 by the embedded detector method for the stator winding, 95 by the embedded detector method for the stator core, 100 by the resistance method for the field winding, and 75 by the infrared method for the slip rings. For parts not in contact with windings, the temperature rise shall not damage the insulation of the part itself or of any adjacent part. A note to the table states that the limits already take into account the effect of frequent starting of the motor-generator.

6.1.2 The stator and rotor insulation shall use insulating materials of thermal class 155 (F).

6.1.3 Where the rotor insulation uses materials of thermal class 180 (H), the temperature rise of the field winding measured by the resistance method shall not exceed 125 K.

6.2 The measurement of the temperature rise of the stator winding and stator core shall meet the requirements of GB/T 7894.

6.3 Where the rated operating conditions of the machine depart from those of Clause 4, the temperature rise limits shall be corrected in accordance with GB/T 755.

6.4 In normal operation the maximum bearing temperature measured by the embedded temperature detector method shall not exceed 80 °C for babbitt-lined thrust bearing pads and 75 °C for babbitt-lined guide bearing pads. The embedment depth of the temperature sensors should be 20 mm to 30 mm from the friction surface.

7 Operating characteristics and electrical connection

7.1 The capability of the motor-generator to withstand unbalanced current and overcurrent shall satisfy GB/T 7894. The machine shall withstand the short-time overload and rapid speed rise caused by load rejection of other units on the same waterway, the short-time overload not exceeding 150 % of rated load. In motoring operation the machine shall withstand 150 % overtorque for 15 s without losing synchronism.

7.2 When starting in motoring operation the machine shall meet the requirements for starting by static frequency converter (SFC) and for back-to-back synchronous starting.

7.3 Synchronising to the network, earthing, the neutral point lead, phase sequence and the stator winding shall comply with GB/T 7894.

8 Insulation system

8.1 The dielectric dissipation factor of the stator bars or coils at ambient condition and its increment shall comply with Table 2. The table sets a limit of not more than 1 % for tan delta measured at 0.2 times the rated line voltage, and a limit of not more than 0.5 % for the increment between 0.2 and 0.6 times the rated line voltage, the increment being the difference between the value at 0.6 times and the value at 0.2 times the rated line voltage. Notes to the table state that the rated line voltage is expressed in kV and that testing is carried out on 100 % of the items.

8.2 Where the design of the winding is such that the upper-layer winding cannot be tested in groups by voltage withstand test after being placed in the slots and wedged, that stage of the voltage withstand test may be omitted.

8.3 The insulation system of the windings, the voltage withstand test, the insulation breakdown test, the voltage endurance test, the thermal cycling test of stator bars and coils, and bearing insulation shall comply with GB/T 7894.

9 Mechanical performance and design

9.1 In generating operation the direction of rotation should be clockwise viewed from above.

9.2 The machine shall withstand the maximum design speed for 5 min without harmful deformation or damage. The maximum design speed is given by the technical agreement between supplier and purchaser, or defined by the pump-turbine supplier, and corresponds to the greater of the maximum runaway speed and the maximum transient speed of the pump-turbine.

9.3 The first-order critical (bending) speed of the unit shall be not less than 120 % of the maximum design speed. For units with a speed of 500 r/min and below, the first-order critical (bending) speed should be not less than 125 % of the maximum design speed.

9.4 Vibration analysis for steady-state and transient duties and calculation of the natural frequencies shall be carried out for the structural parts of the machine, the latter satisfying GB/T 7894.

9.5 The machine as a whole and its components shall have sufficient strength and stiffness so that under normal, special and extreme duties the stress, deformation, vibration, run-out and displacement remain within a reasonable range and satisfy the relevant technical documents, without harmful deformation or damage. Normal duties include steady-state operation (rated load, part load, leading and lagging power factor operation), transitions between operating modes and starting and stopping; special duties include load rejection in generating operation, loss of supply in motoring operation and emergency shutdown; extreme duties include a single-phase-to-earth short circuit of the stator winding, sudden two-phase and three-phase short circuits, short circuit of half the rotor poles, faulty synchronising, earthquake and operation at the maximum design speed. Working stresses shall not exceed the specified maximum permissible stresses; components subject to alternating, vibratory or impact stresses require fatigue analysis with an adequate safety margin. Working stress and deformation of the main components may be calculated by classical analytical formulae or by the finite element method, the latter being preferred for important components with complex loading in large, high-speed machines, such as the stator frame, brackets, rotor centre body, poles, rotor rim, main shaft and shaft system. The mean stress obtained by either route should not exceed one third of the yield strength of the material under normal duty, two thirds under special duty and three quarters under extreme duty. Local stresses calculated with a linear elastic material model should generally not exceed 1.5 times the yield strength; above that value a further assessment against criteria such as FKM or ASME is required. For loaded parts whose stress does not alternate during starting, stopping or mode changes, the permissible stress may be raised appropriately.

9.6 Within a mechanical life of 40 years the machine shall withstand a total of not less than 116 800 starts and stops, one cycle consisting of one starting and one stopping process, with a permitted maximum of not less than 10 starts and stops in a single day.

9.7 Within a mechanical life of 40 years the machine shall withstand 500 full-load load rejections and three occurrences of the maximum design speed.

12 Structural requirements

12.1 The structural design shall satisfy GB/T 7894 and suit system peak shaving, valley filling, frequency regulation, phase modulation, emergency standby, mode transitions and frequent starting and stopping.

12.2 A suspended or semi-umbrella configuration may be used. The general arrangement shall suit the dismantling method of the pump-turbine. Where upward dismantling is used, the lower bracket and the removable parts of the pump-turbine shall be able to pass through the inner diameter of the stator core during erection and overhaul; where middle dismantling is used and the lower bracket is load bearing, the lower bracket shall be able to carry the lifting of heavy parts such as the pump-turbine head cover and runner without harmful deformation. It should be possible to replace rotor poles and stator bars without lifting the rotor or removing the upper bracket, and to inspect the stator winding end windings and the stator core conveniently.

12.3 The stator frame and the core clamping structure and its process shall suit frequent starting, stopping and mode transitions and prevent loosening and buckling of the core. Where through bolts are used to clamp the stator core, full insulation between the through bolts and the core shall be provided to avoid short circuits between them.

12.4 The fixing arrangements and materials for the stator bars in the slots and at the ends shall prevent loosening, sinking and wear of the bars under the long-term action of thermal stress and vibration during frequent starting and stopping and under normal and abnormal duties.

12.5 The poles shall use a structure and measures that prevent harmful deformation of the pole coils. The design of the pole coils and of the interpole connections shall withstand the thermal stress and vibration in service and the centrifugal force at load rejection or at maximum design speed, and shall satisfy the fatigue strength requirements.

12.6 Where the lead-out of the pole coil has a bent structure, its bending radius should be not less than four times the thickness of the lead-out.

12.7 To prevent breakage of the pole insulation support plate by centrifugal force, the support plate shall be fixed relative to the pole core. The insulation between the pole coil and the core shall satisfy the creepage distance requirement; L-shaped corner insulation or effective sealing with insulating material is preferred.

12.8 Where a shrink-fitted slip ring rotor structure is used, the slip ring rotor shall not loosen under any operating duty or during overhaul. The interference calculation shall take full account of the centrifugal force of the slip ring rotor, the radial force of the guide bearing, the fitting length between slip ring rotor and shaft, and thermal deformation.

12.9 The thrust and guide bearing structures and their lubricating oil circulation and cooling systems shall suit operation of the unit in both directions of rotation and hot starting of the unit.

12.10 The structure and geometry of the thrust and guide bearing pads shall ensure that an oil film forms readily in both directions of rotation.

12.11 The thrust bearing shall be fitted with a high-pressure oil injection device for use during starting and stopping. During starting, the device should be allowed to be taken out of service when the speed reaches 50 % to 80 % of rated speed. A standby pump shall be provided for the high-pressure oil injection device.

13 Ventilation and cooling system

13.1 The stator and rotor should use a closed axial and radial ventilation cooling system without added fans, and the ventilation and cooling system shall suit operation in both directions of rotation.

13.2 The air coolers shall have a heat exchange margin of 10 % to 15 %. Where external circulating oil coolers are used for the bearings, the oil coolers should be arranged on an N plus 1 basis.

13.3 When the cooling water of the bearing oil coolers is interrupted, the unit shall be allowed to run at rated speed and rated load for 10 min without any damage to the thrust and guide bearings.

13.4 The working water pressure of the air coolers and oil coolers is generally designed for 1.0 MPa to 2.5 MPa, the actual working pressure being stated in the technical agreement between supplier and purchaser. In the static pressure test of the coolers, the test water pressure is 1.5 times the working water pressure held for 30 min, after which the pressure is reduced to the working pressure and held for 30 min without a pressure drop.

13.5 The pressure resistance of plate heat exchangers follows NB/T 47004.1.

13.6 The ventilation cooling of the slip rings and carbon brushes should be designed together with carbon dust extraction.

14 Braking system

14.1 The braking system shall suit operation of the unit in both directions of rotation and frequent starting and stopping.

14.2 Electrical braking and mechanical braking shall comply with GB/T 7894.

14.3 The mechanical braking device shall not produce chemical substances harmful to the environment and shall be fitted with a dust collection device. The brake ring shall be designed to be removable. The brake pads shall be made of wear-resistant and heat-resistant material with a normal service life of not less than 5 years.

14.4 A hydraulic jacking system shall be provided. It may be combined with the braking system or used separately, for example with a disc brake system. The system shall be able to lift the weight of the rotating parts of the unit and to lock the rotor safely in the raised position.

15 Devices and components of the control and protection system

15.1 The devices and components of the control and protection system used shall comply with GB/T 7894 and GB/T 11805.

15.2 The number and location of the temperature detectors for the coolers and bearings are given in Table 3: two per air cooler, one on the cold air side and one on the hot air side; two per thrust bearing pad, one on the oil inlet side and one on the oil outlet side; two for the thrust bearing oil, one on the cold oil side and one on the hot oil side; two per guide bearing pad, one on the oil inlet side and one on the oil outlet side; and two for the guide bearing oil, one on the cold oil side and one on the hot oil side.

17 Marking

In addition to complying with GB/T 7894, the rating plate shall carry the following further items for motoring operation: rated power in MW; rated voltage in V; rated current in A; rated power factor; rated excitation voltage in V; and rated excitation current in A.

19 Factory and site tests

19.1 The items of the factory tests shall comply with GB/T 7894.

19.2 The items of the site tests shall comply with GB/T 7894 and GB/T 18482. Where necessary, a charging capacity test, including measurement of the temperature rise of the end structure, and a black start test may be carried out.

21 Trial operation and guarantee period

21.1 Before the machine and its auxiliary equipment are put into commercial operation after erection and testing on site, a 15 d acceptance trial run shall be carried out, in accordance with GB/T 18482.

21.2 Once the unit has passed the 15 d trial run and all defects found have been dealt with during shutdown, it is ready for handover. The unit and the associated electromechanical equipment shall be handed over in good time as provided in the technical agreement between supplier and purchaser, the preliminary acceptance certificate shall be signed, commercial operation shall begin and the guarantee period of the equipment shall start to run. The guarantee period shall comply with GB/T 7894.