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 Electric Motor Repair
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 Industrial Pump
 Balancing Services
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 เครื่องกำเนิดไฟฟ้า
 ออกแบบสร้างเครื่องจักร
 Laser Shaft Alignment



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บทความที่หน้าสนใจ
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วงจรกลับทางหมุนมอเตอร์ 1เฟส
มาตรฐาน ISO-2372
การติดตั้งตลับลูกปืน
The Basics of Balancing
การทดสอบค่าความเป็นฉนวน
Surge Comparison Tester
Automatic Transfer Switch (ATS)






9 MECHANICS CO.,LTD.

1/9 หมู่ที่12 ต.บางพลีใหญ่ อ.บางพลี จ.สมุทรปราการ 10540

Tel : 02-751-0755 Fax : 02-337-3426

E-mail: savemotorservice@gmail.com

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E-mail: savemotorservice@gmail.com

Emergency Call : 08-6770-0066 , 08-6667-8789

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Surge Comparison Tester
Surge Comparison Test (อ่าน 6707/ตอบ 1)

Principle of Surge Comparison Tester
The Surge Comparison tester checks the strength of ground insulation that consists of enameled insulation. It detects the insulation failures such as turn-to-turn shorts, layer-to-layer shorts, coil-to-coil shorts, winding-to-winding shorts, and phase-to-phase shorts. Open circuit and ground detection are other benefits of surge testing.

The Surge tester uses the principle of impedance balance to test the quality of electrical windings.The Surge tester works as a capacitive-discharge system. A capacitor is charged with high voltage and then discharged into the winding, through a solid state assembly. This sequence is repeated thus stressing the insulation of the winding with high voltage pulses.

The resulting voltage decay pattern of two winding is then displayed on the CRT. The waveform pattern will be perfectly superimposed for good windings but in case of a defective winding a double wave pattern will appear on the screen as one wave pattern from the good winding plus the erratic pattern from the faulty winding.

Surge Test Voltage to be applied = √2 × (2×E + 1000)
where E is the operating voltage of the rotating machine

The Surge Tester stresses the whole winding system as the current is applied as series of pulses. The voltage of these pulses rises in microseconds and produces a voltage distribution across the coil. For instance, when the pulse has penetrated to turn number 10, it may be at 2000volts while other turns (20,30 etc) have not been pulsed. It is at a lower voltage and if this difference is greater than Dielectric strength of the turn insulation, one or more turns may be shorted out of the circuit. If this shorted circuit is compared to the master winding, the two patterns will not match

  

Principle of Bar-to-Bar Test

The bar-to-bar test is used to test the armatures of Large DC motors without over-stressing the group insulation. Historically, span test method was used to test the DC Armatures by applying a very high test voltage across the coils to generate required inter-bar voltage. High voltages could result in break down of ground insulation of the first coil in the series. 
The Bar-to-Bar test method eliminates the limitation of span test method by applying High Surge current at significantly low voltage to produce the necessary inter-bar voltage across the adjacent commutator bars. Therefore the danger of ground insulation break-down is significantly reduced as the Bar-to-Bar test voltage never exceeds 1000 volts. 
A special low impedance cable and test head assembly is required to perform the Bar-to-Bar test in order to apply the Inter-bar voltages across different types of armatures. 

·  100-300 volts for small armatures

·  200-500 volts for medium armatures

·  500-800 volts for large traction armatures

Principle of DC Hi-Pot Test

The DC Hi-Pot test is extremely important to identify the deterioration in the insulation as early as possible to take corrective measures. The high potential is applied between isolated parts of a circuit or a product, the behaviour of electrical parameters such as Leakage current helps identify broken or poor insulation, stray wire strands or braided shielding, spacing problem between terminals, tolerance errors, etc. During the Hi-Pot test, a high voltage is applied to the device under test (DUT) that causes a small leakage current (microamperes) to flow from the conductor and insulation. This small leakage current depends on three main factors i.e.
(i) test voltage
(ii) system capacitance and
(iii) temperature of the material
The leakage current is also a combination of three sub-currents :
I) Conductive leakage current. Conductive current is a small current that normally flows through insulation, between conductors or from a conductor to ground. This current increases as insulation deteriorates and becomes predominant after the absorption current vanishes.
II) Capacitive charging leakage current. When two or more conductors are run together in a raceway, these act as a capacitor. Due to this capacitive effect, a leakage current flows through conductor insulation.
III) Polarisation absorption leakage current. Absorption current is caused by polarisation of molecules within the dielectric material.
The Hi-pot test therefore helps in making informed decision on the safety and quality of electrical circuits and eliminates the possibility of having a life-threatening short-circuit or short-to-ground faults.

Principle of Rotor Test

The Rotor tester uses the principle of electrical and magnetic effects caused by the circulation of induced currents into the bars of a rotor, which is made to turn at a constant speed, with in a magnetic field produced by a permanent magnet. The induced magnetic field produced by permanent magnet, acts on one slot at a time. The direction of magnetic field is such that the turns of a moving rotor cut the lines of force normally. 
The induced currents, which are proportional to the field intensity (distance of magnet from the rotor, on the speed of rotation constant) & on the rotor characteristics, produce magnetic fields, the symmetry of which enable a clear observation of the turns in the short-circuited condition. A fixed probe subjected to the magnetic fields produced by the rotor under test, provides the signals, which after being amplified, are applied to the monitor. 
The synchronized sinusoidal wave pattern from the rotor bars is displayed on the monitor screen. The waveform identifies typically occurring faults in the rotor bars & there is a distant correlation between the result of the inductive test of the rotor bars & the starting torque of a motor.


Fig. shows following defects of the rotor:-

·  A - defect due to Broken Bar

·  B - defect due to Bar to Bar shorting

·  C - defect due to Blow Hole or High Bar Resistance

·  D - Perfect rotor portion

·  E – defect due to Skew Angle

Benefits

User friendly front panel controls
Lightweight, compact, rugged and solid state design
Highly sensitive fault detection capability – It detects
even a single turn short in the coil
Test leads insulated to 45KV rating
Leads energized warning indicator
Bright sharp CRT display to analyze the faults easily
1phase/3phase Test Select Switch

Applications

This tester is widely used for testing newly and rewound
motors. It helps in finding and predicting the faults in
motors before it actually happens.
This tester is extremely portable that can be easily used
in the motor shop and in field to test the following :
- 1φ & 3φ windings
- LT coils
- AC,DC motors
- Stators
- Transformer coils
- Solenoids & Chokes


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ความคิดเห็นที่ 0
A plgleinsay rational answer. Good to hear from you.
Mahmud email
(03/08/2556 00:20:15) IP. 91.128.228.xxxxxx
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