Abstract:
The main focus is on the factory routine inspection test items and parameter assessment criteria for three phase motor
The standard control of DC resistance, insulation resistance, frequency withstand voltage and inter-turn waveform parameters of three phase motor is described.
Emphasis is placed on the methods and basis for determining the no-load current, no-load losses, blocking current and blocking losses of three phase motor
Keywords:
routine inspection tests; insulation resistance test; running performance; no-load current; no-load losses; blocking current; blocking losses.
介绍
The purpose of the routine inspection test of three-phase asynchronous motors is to determine the conformity of the actual load running performance of the motor by testing and checking the electrical insulation performance and running performance of the three phase ac motor.
Different electric motor manufacturers combine their own process characteristics and type test reports, presume the relationship between the routine inspection test parameters of three-phase asynchronous motors and the main performance of the electric motor, so as to determine the specific criteria for routine inspection test assessment of the three phase motor.
1. Standard control principles for routine inspection power supply test of three phase motor
There are two main types of standards in the routine inspection test of electric motors:
the electrical insulation performance and the reference standard for the test items of electric motor running performance.
The electrical insulation performance standard is the basis for the qualification of the insulation performance of the motor winding.
Generally there are clear national or industry standards, mainly including insulation resistance, inter-turn test, voltage resistance test and other items, which can clearly give the degree of compliance with the technical conditions, there is no uncertainty in the judgment.
The three phase ac motor running performance standard for the power supply test is a standard to confirm whether the electric motor running performance is in accordance with the product technical conditions.
If the test value is within the standard range, it can be confirmed that it is close to or has reached the level of the technical conditions of the product.
But the degree of conformity with the technical conditions cannot be clearly given.
In addition to DC resistance, the other four groups of values directly determine the key performance parameters of the testing motors, and the relationship between the parameters is sometimes contradictory.
For example, the blocking current is an important indicator of the motor test, too large will exceed the limit itself, too small will cause a small blocking torque.
At the same time, the blocking torque is also an important indicator of the induction motors.
So the running performance assessment standard must be determined in an integrated manner.
The electrical insulation performance and induction motors running performance of each individual product varies to a certain extent due to raw materials and process fluctuations.
In order to control the conformity and consistency of product quality, key special processes are defined in the motor manufacturing process:
the stator dipping process and the rotor aluminium casting process.
Taking into account the process fluctuations in the quality of the raw materials used, the inevitable errors in the production process and processing, as well as the influence of normal uncertainties such as test measurement errors, the permissible range of fluctuations in test data needs to be reasonably determined during routine inspection tests.
Ensure that the performance of induction motors that pass the routine inspection meets the technical requirements of the product.
2. Routine inspection test of electrical insulation resistance
Routine inspection test of electrical insulation performance of three-phase asynchronous motor, usually first insulation resistance test, according to the rated working voltage of many motors, select the test equipment corresponding to the working range and qualified standards, test qualified and then AC withstand voltage test of motor condition, in the case of no breakdown according to the scope of Table 1, assessment of the insulation leakage current under the specified standard high voltage.
The leakage current is within the allowable value, then do the inter-turn test.
For the machine wound and embedded stator, the absolute difference limit can be set at 4% to 5%, the field testing area difference limit can be set at 2% to 3%, for the artificially wound rotor and embedded stator or the unstable material, the absolute difference can be set at 8% to 10%, and the area difference can be set at 3% to 4% or so.
Each index is qualified, which means the motor winding is well insulated and the insulation test is qualified and conforms to the national standard of the running amps.
The electrical insulation performance directly affects the operating life of the motor. A poorly insulated motor winding has serious quality risks and will cause insulation breakdown and burn out the winding coil in the hot state during good motor load operation.
Table 1 Reference values for insulation leakage currents of electric motors with different seat numbers
| Frame number | ≤H180 | H200~225 | H250~280 | H315 | H355~500 (loose inlay winding) | H355~500 (Formed winding) |
| Leakage current (mA) | 0~10 | 10~20 | 20~30 | 30~50 | 50~100 | 30~50 |
3. Standard implementation of three phase motor running performance routine inspection test parameters
The normal fluctuation range of three phases motor performance parameters needs to be measured over a long period of time for multiple motors, as an important basis for the development of routine inspection test standards.
Table 2 shows the normal fluctuation range of the operating performance parameters and the fluctuation limit of the reference standard of the routine inspection test parameters for the ordinary IE3 series electric motors produced by electric motor manufacturer.
Table 2: The fluctuation range of the operating performance parameters of IE3 series motors and the fluctuation limits of the reference standard
| Performance parameters | Windings DC resistance | No-load current | No-load loss | Blocking current | Blocking torque | Blocking losses | Maximum torque | Minimum torque | Full load efficiency | Power Factor | Turnover rate | Full load temperature rise |
| Normal range % fluctuation | ±2 | ±4 | ±8 | ±4 | ±8 | ±3 | ±3 | ±2 | ±1 | ±1.5 | ±2.5 | ±3 |
| Routine check control limits % | ±3 | ±5 | ±10 | ±5 | ±10 | ±5 |
4. The relationship between the parameters of the routine motor running performance test and the main running performance
The parameters of the routine inspection and test of the running performance of three-phase asynchronous motors are divided into no-load current, no-load loss, blocking current and blocking loss, which directly affect the key running performance of the good motor.
If the no-load current is large, the power factor is low; if the no-load loss is large, the efficiency is low.
If the blocking current is large, the blocking current at rated voltage may exceed the assessment standard; since the blocking torque is proportional to the blocking current, a small blocking current may cause the blocking torque at rated voltage to fail to meet the standard requirements.
Large blocking loss, low efficiency; small blocking loss, may cause the maximum torque can not reach the standard requirements.
5. The method of determining the standard for routine inspection test data of three-phase asynchronous motors
The development of the qualified range of the routine inspection test of the operating performance of three-phase induction motors is generally divided into the qualified area method and the upper and lower limit method.
The qualifying zone method uses the motor principle and mathematical calculation methods to derive a series of relational equations, and then substitutes the prototype test data and test standard values into these relational equations to derive the control formula.
When used, the actual measured data is substituted into the corresponding control formula and a comprehensive decision is made as to whether the motor is qualified or not.
This method has high control accuracy, but is more cumbersome to calculate and use, and can sometimes cause misjudgements due to the large range of criteria.
The upper and lower limit method is based on the test data of the qualified prototype and the test standard to give the range of permissible fluctuation of each test data, called single value "upper and lower limit method".
Compared with the qualified area method, the control accuracy is slightly worse, but the calculation and use of simple and convenient, more widely used.
The upper and lower limits method is based on the following principles and considerations.
(1) as much as possible to summarise the type test data of the qualified prototype
calculate the average value of the relevant items and fluctuation range (maximum and minimum values).
(2) for no-load current,
if the maximum value corresponds to the power factor has reached the minimum limit of the assessment, the maximum value is the factory standard no-load current of the maximum limit.
No-load current may not be subject to a minimum limit.
If deemed necessary (e.g. to prevent the use of the wrong rotor or air gap is too small to cause sweeping), the above statistics can be relaxed by 3% of the minimum value of no-load current, as the factory standard no-load current of the minimum limit value.
3) No-load losses can be set at a maximum value only.
Considering that the value is influenced by the running time, test environment (mainly ambient temperature) and other factors during the simple factory test, it can be increased by about 10% on the basis of the maximum value of the above-mentioned prototype data.
If the factory test is higher than the maximum value given, the running time of the motor testing should be extended appropriately to obtain a more stable no-load loss, and then compare and judge.
(4) The impact of the test environment on the blocking current and blocking loss is relatively small
so the control range of the upper and lower limits should be determined in strict accordance with the fluctuating statistical values of the prototype.
If calculated according to the statistical average of the prototype, the blocking current is 95%~105% of the statistical average of the prototype; the blocking loss is 90%~110% of the statistical average of the prototype.
(5) pay special attention to the motor routine inspection test before the installation of the motor winding shield.
while the type test is carried out after the complete assembly of the machine, so for the determination of the no-load loss standard should be necessary to amend.
6. concluding remarks
The routine inspection test of three-phase asynchronous motor can, to a certain extent, assess the insulation tester performance, temperature rise, efficiency, power factor, starting capacity and other major performance indicators of the motor through electrical performance and operational performance inspection.
The qualification or otherwise directly affects the operational performance of the motor.
The maintenance experimental personnel should master its limit value law, ensure that the routine inspection test qualified motor factory, to the existence of problems with the motor analysis of the causes of failure, maintenance, so as to ensure that the performance indicators of the motor in line with the product standard requirements.
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