Current injector for testing automatic circuit breakers is intended:
- to test the functionality and control of ampere-second characteristics of AC circuit breakers in the range of 20A up to 3kA, and measuring and storing of values of time and current flowing through the circuit breaker, hereinafter CB;
- for the verification and certification of the current, measurement and protection current transformers with primary current;
- for testing and calibration of current relays;
- for testing and calibration of thermal current relays;
- to check the fuses;
- can be used as a source of regulated AC current up to 3kA in a low-impedance power circuits for laboratory works.
Having located the cable fault operator must:
a) determine the type of fault in accordance with previous section (Classification of faults and damages in power cables);
b) determine the distance to fault with the help of a low-voltage, or high-voltage time-domain reflectometer TDR (ISKRA-3M);
c) trace the cable line with a sound frequency generator (GZCH-2500) and the induction receiver (POISK-2006M or P-806) (ie, to determine the route of underground cable on the ground surface) and to limit fault area (ie, the area within which located a FP);
d) locate and pinpoint the FP within area of fault.
The solution of this task depends on type and characteristics of equipment available and qualifications of operators. Next we will consider some techniques of the methodic.
1. Induction search method
Induction method for cable fault location lies in the fact that during passing current through a cable from the sound frequency generator (GZCH-2500) around the cable formed magnetic field. The nature of distribution of this field depends on many factors (cable structure, the connection method of the generator, a type of fault, presence of a cable sheath contact with ground etc.).
The induction sensor of receiver (POISK-2006M or P-806) transforms this induction (magnetic) field into electrical signal, which is being amplified, selected on frequency and converted into sound by headphones. Under certain conditions, the magnetic field of cable fault decreases sharply, which is indication sign of fault during cable fault location process.
To find a route of a cable line and point of fault with induction method the receiver package includes a remote inductive sensor with hand holder, and inside the receiver has resonant narrowband amplifier.
Inductive sensor consists of a cylindrical multi-turn coil, winded on ferrite core. It is important to understand that such sensor, with respect to the variable magnetic field, has directional properties, namely: the output signal of the sensor will be maximized when the magnetic field lines are perpendicular to the coil plane (or, in other words, the magnetic vector field coincides with the axis of the sensor). The signal will be minimal or absent, if the magnetic field lines are parallel to the plane of the coil (ie, the magnetizing force vector is perpendicular to the axis of the sensor).
2. To find a route of underground cable GZCH-2500 is being connected between core and sheath, according to scheme (Figure 1).
Depending on specific damages and faults, all power
cables can be divided into two main groups: with sheath (shielding) (usually
grounded at both ends) and without it.
Cables with shielding may or may not have an extra metal armor in the form of a spiral steel tape, which protects the cable from mechanical damages. These cables called armored.
The most common fault (and hardest to define) is a type of spark breakdown damage or short-circuit of one core to sheath. Such damage called single-phase damage.
Breakdown or short circuit between the two conductors is the rarest. Such damage called two-phase damage.
Single-phase cable fault is very common and, in most cases, occurs when cable loaded or during cable testing.
Fault point (FP) is characterized by a certain resistance (Rfp) and breakdown voltage (Ufp.). Depending on the ratio of Rfp. and Ufp., conventionally, this kind of fault can be divided into three types:
a) Rfp. = 0 - 1 Ohm; Ufp = 0-10 V.
In this case, the FP has "reliable" electrical contact between core and sheath, and therefore there is no spark.
Such damage called the solid single-phase short-circuit of cable conductor to its sheath (SSC).
b) Rfp 10-100000 Ohms; Ufp = 1-10 kV.
Only one core of cable damaged, and two others withstand the test voltage. FP is characterized by significant leakage currents (milliamps), but the voltage can be raised within the range 1-10kV, while the FP sparks or arcing. This type of damage called "single-phase leakage".
c) Rfp = 1-100 MOhm; Ufp = 10-50 kV.
In this case, almost no current leakage, but above a certain voltage cable breakdowns with a spark in a fault point.
This type of damage called "intermittent breakdown"
Thus, a common feature of the single-phase leakage and intermittent breakdown is the presence of a spark in a fault point during the presence of voltage in cable, and the sound of the spark. Both of these cases can be grouped under the title "sparked single-phase breakdown".
UPZ - 450/2000 relays and circuit breakers testing device intended for:
- Testing and adjusting of simple relay protection, which already installed on power plants, substations, industrial-governmental enterprises or laboratories.
- Testing and adjusting automation elements (electromagnetic relays, contactors, motor starters, etc.).
- Testing, commissioning and adjusting automatic circuit breakers.
The device made in a single case, which creates additional convenience during operation. Package contents includes wires, cables to connect items under tests.
Now the model has LCD display.
DET DneproEnergoTechnologies ltd successfully exhibited its products at Elcom 2014 - Ukraine’s major industrial event on smart industrial technologies, power and electrical engineering and energy efficiency.
The 20th elcomUkraine held from 22 to 25 April 2014 at the KyivExpoPlaza in Kiev. The event is organised by the German trade show specialists fairtrade and their Ukrainian partners Euroindex.