CORONA-i XT-281
・Feature
Detect the corona discharge, Display discharge Rate, Decision pass or fail.
 
・Application
Inverter driven motor (IPM, SPM). e.g. motor for EV.
Summary
With progress of power electronics, and the demand of energy saving, the inverter drive motor is produced in large quantities as motors, such as an air-conditioner, a washing machine, and a refrigerator.
In recent years, production started in the cars in addition to home electronics including a hybrid car.
Conventionally, the insulation test of a motor has been done with a direct current and commercial frequency.
However, since repetition impulse voltage is added from an inverter, a new test method and equipment are required.
This equipment applies actual inverter repetition impulse voltage and the same test voltage, does an electric discharge examination, detects spark discharge (flashover) and corona discharge (partial discharge), and evaluates insulation performance.
Since spark discharge consumes energy with light and sound, it produces big damage on target equipment and parts, and it becomes poor in an instant or a short time operating it.
On the other hand, it generates by ionization of air and the action of corona discharge is weak. Therefore, it is rare to result in a defect of operation for a short time.
However, insulation deteriorates with progress of time by oxidization by the ozone which occurs by corona discharge and damage by heat. And spark discharge occurs and operating becomes a defect operation.
Feature
Detect the corona discharge, Display discharge Rate, Decision pass or fail.
Application
Inverter driven motor (IPM, SPM). e.g. motor for EV.
Specifications

 

Open output frequency 50kHz
Test signal frequency Intermittent damped sine wave
Test signal cycle 500 times/sec
Open output voltage 0.5kVpeak to 5.0kVpeak
Testable device Capacitive 2nF or less
Inductive 200u H to 3mH
Display Discharge Rate 0 to 100%
Flashover 0 to 127count
High Voltage 0 to 5kVzero-peak
Monitor output Flashover, +High Voltage, -High Voltage
Peak Current, Sync, Discharge Monitor
If corona discharge exceeds a setting rate or spark discharge exceeds a predetermined number within a set period on setting voltage, it will judge with a defect.

 

Dimensions Main equipment: 430(W)×470(D)×180(H) mm Mass17kg
Probe box: 430(W)×470(D)×180(H) mm Mass15kg
Power supply AC 100V,AC 220V(select) ±10%
Basic operation
Basic circuit

If gate voltage is turned on for a definite period of time, the current, which flows into IGBT with progress of time, will increase.
The electric energy, which flows then mainly, turns into magnetic energy, and is stored in built-in inductance and the inductance of an examination subject.
If IGBT is turned off, magnetic energy will be transformed into electric energy and will serve as high voltage. And it resonates in the circuit which consists of built-in inductance, built-in capacitance, and a test device, becomes an oscillatory wave form, and decreases.
Moreover, also in a capacitive case, a test device is like between winding cores can cause a damped sine wave due to the internal inductance.
Voltage and current of each part by simulation
IGBT ON time:50us
D.U.T Inductance:200uH
Applied D.C Voltage:100v

Discharge detection
This equipment detects the existence of corona discharge and spark discharge for every test signal applied intermittently.
 
 ・Spark discharge
  Discharge is detected from a rapid change of the test signal voltage applied to a test device.
If discharge is detected, it will indicate as a count (0 to127).
 
 ・Corona discharge
  The discharge signal included in the current, which flows into the test device, is detected.
If discharge is detected, it will indicate as the discharge rate (0 to 100%)

 

Discharge rate
In order to decide the conditions of insulation tests, such as an insulator, a coil, etc. to repetition impulse voltage, it is necessary to get to know partial discharge inception voltage (RPDIV) and extinction voltage (RPDEV).
In an electric discharge start (stop), if it becomes a value with the voltage to apply, it will not necessarily discharge 100%(0%) suddenly. The number of times of discharging gradually increases (decrease).
However, do not increase (decrease) smoothly, and it discharges, or it stops and increases (decrease) intermittently and irregularly.
The situation is briefly shown in the following figure.
RPDIV is defined by 2006 IEC61934TS as the minimum impulse voltage from which the number of times of partial discharge impulse generating will be more than 50% to the number of times of a repetition voltage impulse.

XT-281 has a function, which displays the rate to discharge to the impulse applied repeatedly.
A moving average is calculated by the damping time constant for 0.1 second, and the rate to discharge is continuously indicated as analog meter and a numerical value.
The following examination can be performed by this function.
 
  A test condition is set to <50%>
     ↓
  Voltage is increased
     ↓
  Discharge Rate exceeds <50%>
     ↓
   Stop
     ↓
  The voltage at that time is displayed.
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