Finally, this ergonomic tester is equipped with a bright LED torch, GS38 probe tip shrouds, and an IP64-rated housing. The Megger TPT420 is also supplied with a carry pouch. FIGURE 4: Surge test voltage vs the dielectric strength of a 460 V motor and typical voltage spikes it sees in service But what overall voltage is necessary to show up these turn-to-turn faults, and will this voltage be harmful if applied to a fault-free motor? How do the test voltages relate to the dielectric strength of the windings? On older style CCVTs, the potential terminal is typically accessible. However, for modern CCVTs such as those supplied by Trench, the potential terminal is inaccessible. Even in these cases, however, C2 can still be tested. CCVTs have a potential ground switch that provides the means to ground the potential terminal. With the potential ground switch closed, the carrier terminal can be energised, a low voltage lead connected to the line terminal (top of C1), and a C2 test performed in the GST-guard mode. Note that the carrier terminal must be disconnected and isolated from ground potential and the drain coil (also, if applicable, from any accessory leads) for the C2 test. In addition, the test voltage (typically 500 V) used to energise the carrier terminal must not exceed the voltage rating of the terminal. In summary: Inside the voltage tester, this current passes through a known resistance. The voltage drop across this internal resistance is then measured and displayed on the tester's meter or screen. This provides the user with a reading of the voltage present. In some cases, for basic testers, this voltage may simply trigger a light or a sound to indicate the presence of voltage rather than providing a precise numerical value.

A bad turn will short and this will be shown by a jump in the ringing frequency of the coil (it becomes in effect a ‘different’ coil at this point in the test). Large frequency jumps can be clearly seen on the tester display, but the instrument’s software also uses mathematical analysis to reveal anomalies that are less easy to spot by eye. The Megger TPT420 LCD/LED Two-Pole Voltage Tester is an AC/DC voltage indicator. It can detect and measure voltages between 12 and 1000V AC and 12 and 1500V DC. The detected voltage range is indicated on the LED scale while the numerical reading is displayed on the LCD.

What’s Included?

In addition to this, the Megger TPT420 LCD/LED Two-Pole Voltage Tester features a Continuity function which will alert the user to the presence of continuity between 0 and 500kΩ via a visual and audible alert. The Megger TPT420 LCD/LED Two-Pole Voltage Tester will also issue an audible alert upon detection of voltage and will continue to warn the user of dangerous test voltages even when its batteries have expired. This voltage tester has a safety rating of CAT IV 1000V. The basic insulation tests just described can be usefully augmented by adding PF measurements at different frequencies and a tip-up test. A PF test at 1 Hz specifically, provides a better indicator of developing issues, facilitating early detection. 1 Hz PF is particularly sensitive to moisture contamination, a commonplace CCVT failure mode. Narrowband DFR tests include power factor tests at several discrete frequencies, including 1 Hz up to 505 Hz. In some circumstances, the CVD capacitive reactance can resonate with the magnetizing reactance of the inductive voltage transformer and the compensating reactor cores. This unwanted effect is called ferro-resonance and can give rise to large and damaging voltages across the inductive and capacitive elements. To avoid this, a ferroresonance damping circuit is installed in parallel with one of the secondary windings. And it’s the same with a surge test generated by a Baker DX tester. It applies a voltage and rise-time to enable you to see the inter-coil response, but with a signal controlled in voltage, time and energy, so that the impact on the motor is similar to the spikes that the motor receives as a result of typical power-system variations during everyday operation. At its core, a voltage tester is a simple device designed to indicate the presence of electrical voltage in a system or a component. The underlying principle lies in Ohm's Law. This states that the current passing through a conductor between two points is directly proportional to the voltage across the two points.

The instrument has abright, integrated LED torch to helpyou when working in poorly lit environments and, it is safetyrated at CAT IV 1000 V with an IP64 housing, and conforms to the latest IEC/EN 61243-3 and DIN VDE 0682-401 standards. For compliance, GS38 probe tip shrouds are provided as standard, along with a protective storage and carry pouch. In fact, it will typically take the pulse 100 ns to travel from one coil-turn to the next, which is equal to the rise time of the pulse. The result is that the pulse produces a significant voltage difference between adjacent turns of the coil, something that it is impossible to achieve with any other test technique. The surge test will, therefore, reveal turn-to-turn insulation weaknesses. Basic insulation testing, PF tests at 1 Hz, and tip-up testing can be performed with the Megger Delta4000 test set and, with the addition of a DMM, a basic ratio test can be carried out. Ratio validation to an accuracy of ±0.1 % can be carried out with the Delta4000 test set and an accessory. The Megger MRCT test set can also perform basic insulation testing and ratio validation to an accuracy of ±0.1 %, with the added benefit of being able measure the overall burden of the CCVT, thus ensuring that the burden rating has not been exceeded. When testing between phase and earth on any circuit protected by an RCD, RCBO, and Safety Breaker, the TPT420 is designed to work below the tripping threshold of these devices to help avoid unintentional disconnection. The phase rotation indication test has been simplified, which now avoids the crossing of the test probes. The TPT420 can also perform a single-pole voltage indication test. The EMU, in addition to an inductive voltage transformer, contains a tuning circuit and protection against ferroresonance (Figure 1). The tuning circuit is a reactor that compensates for magnitude errors and phase shift caused by the CVD, making it possible to have the CCVT with a characteristic on the secondary side that is similar, in terms of error and phase deviation, to that of a purely inductive voltage transformer.

Megger VF5 Voltage Tester Key Features

For a motor in normal operation, which has not endured significant electro-mechanical thinning of the insulation, the surge-test voltage is far below the dielectric strength of the insulation. Power frequency (50 / 60 Hz) power factor / tan delta testing has been the standard for evaluating the condition of solid and liquid insulation in transformers for over 100 years.With the introduction of 1 Hz power factor / tan delta testing, Megger is revolutionizing insulation diagnostics. When testing at 1 Hz, the dielectric losses due to moisture, contamination and increase liquid conductivity are better observed. Power factor or tan delta test at 1 Hz provides superior detection sensitivity to early and advanced insulation deterioration. Combined with power frequency measurement, 1 Hz delivers immediate insulation assessment without the need for trending or proprietary databases. The Megger TPT420 voltage tester is designed to provideelectricians and electrical engineers with an easy-to-use voltage indicating instrument. The meter will continue to warn the operator of dangerous test voltages even when the batteries are exhausted. With both LCD and LED displays, the TPT420provides both AC and DC voltage measurement from 12 to 1000 V AC and up to 1500 V DC. In addition, a continuity function within the range 0 to 500 kΩ, is included and for added safety, continuity, and voltage measurements are also accompanied by an acoustic sounder. CCVT construction varies between manufacturers, models and year of fabrication. Knowledge of the construction is critical when deciding what and how to test. As mentioned previously, some CCVTs are equipped with a potential grounding switch located below C1, at the intermediate voltage terminal (IVT), and a carrier grounding switch below C2 at the low voltage terminal (LVT), as shown in Figure 3. In some CCVTs, however - mainly modern types - the low voltage terminal may not accessible. Understanding the construction characteristics and location of the IVT and LVT is therefore important when determining appropriate connections for testing and deciding whether the ground switches need to be open or closed for the required measurements to be made.

In addition to the unit's adaptable auto-ranging voltage and continuity tests, the Megger MET1000 has a built-in current clamp for AC current measurement to 200 A. With true RMS AC measurements, a phase rotation test, and single pole voltage test built in, the MET1000 is a truly multi-purposeelectrical test instrument, ideal for use in commercial, industrial, and domestic environments. It even comes with GS38 shrouds, provided as standard, to ensure compliance with the latest standards. When the probes of a voltage tester are connected to two points in an electrical circuit (commonly one end to a suspected live conductor and the other to a ground source), a closed circuit or loop is formed. This allows electrical current to flow from the higher potential to the lower potential. On-Line testing – that is, testing while the motor is running – can also be carried out on an as-needed basis with a portable on-line monitor like the Baker EXP4000.

Megger VF5 Voltage Tester Technical Specifications 

Figure 1 provides examples of surge traces for a good winding and a winding that has weak insulation or a turn-to-turn short. The three traces – corresponding to the three phases of the motor’s windings – should overlay as one on the graph but, as can be seen, the trace for a winding with a turn-to-turn short is different from the traces for the other two phases.