1、英文原文Automatic Testing of Advanced Transformer Differential Relays with Multiple Restrained InputsAbstract: Testing of advanced microprocessor based transformer differential relays with multiple restrained inputs presents a significant challenge to the protection engineer. The availability of multipl
2、e protection functions protecting the transformer for different internal, external and system fault or overload conditions make testing of multifunctional transformer protection relays very complicated and time consuming task, which requires specialized equipment. The paper discusses the requirement
3、s for adequate testing of each of the specific protection functions.A report oriented approach to the automatic testing of the multifunction-al multi-restrained transformer differential relay is described as well. The relays are tested for both internal or external faults. Phase-to-phase and phase-t
4、o-ground faults are considered. Hardware requirements and configuration for automatic testing are introduced. Definition of a transformer protection relay as a test object is presented. Different test methods are discussed in the last section of the paper.Keywords: Transformer Protection. Multifunct
5、ional MicroprocessorRelays. Automatic Testing I. INTRODUCTIONTransformers are the most expensive piece of equipment in a typical transmission or distribution substation and are exposed to a wide variety of conditions that can cause different levels of damage. Transformer faults are generally classif
6、ied into four categories :l Winding and terminal faultsl Core faultsl Abnormal operating conditions such as overl voltage, overfluxing and overloadl Sustained or uncleared external faultsAll of the above conditions must be considered individually and the transformer protection package designed accor
7、dingly. To provide effective protection for faults within a transformer and security for normal operation and external faults, the design and application of transformer protection must consider factors such as :l Magnetizing inrush currentl Winding arrangementsl Winding connectionsl Connection of pr
8、otection secondary circuitsThe multifunctional microprocessor based relays must provide adequate protection for any potentially damaging fault or system condition, optimal performance and secure and reliable operation. This means that the relay should trip as fast as possible for any transformer int
9、ernal fault and at the same time should not operate for any external fault condition. Misoperation should also be avoided for any other non-fault condition, while still providing protection for conditions that are harmful if the duration of transformer exposure is significant. Power transformers des
10、ign, size and configuration vary significantly. This, combined with the numerous substation schemes used results in a large number of possible transformer protection applications.To satisfy all the above requirements, todays advanced state-of-the-art transformer protection relays combine multiple pr
11、otection functions and algorithms with multiple restrained inputs.Adequate testing of such multifunctional microprocessor relays and the simulation of the substation environment for different fault and non-fault conditions is a very time consuming task that requires sophisticated test equipment. . T
12、RANSFORMER PROTECTION RELAY FUNCTIONSThe main protection function in a transformer protection relay is the differential protection. Under normal operation steady state magnetizing current and the use of load tap changers result in unbalanced conditions. To accommodate these conditions the differenti
13、al element has a multi-slope characteristic. The initial slope ensures sensitivity for internal faults while allowing for up to 15% mismatch when the power transformer is at the limit of its tap range. At currents above rated, extra errors may be gradually introduced as a result of CT saturation. A
14、different restrained slope characteristic is typically used to compensate for this. However, misoperation of the differential element is possible during transformer energization.High inrush currents may occur, depending on the point on wave of switching as well as the magnetic state of the transform
15、er core. Since the inrush current flows only in the energized winding, differential current results. The use of traditional second harmonic restraint to block the relay during inrush conditions may result in a significant slowing of the relay during heavy internal faults due to the presence of secon
16、d harmonics as a result of saturation of the line current transformers. To overcome this, some advanced relays use a waveform recognition technique to detect the inrush condition. The differential current waveform associated with magnetizing inrush is characterized by a period of each cycle where its magnitude is very small, as shown in Figure 1. By measuring the time of this period of low current, an i
