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In neutral point non-directly grounded medium voltage distribution system, to selectively detect single phase to ground fault remains as a challenge for protection relays. Conventional selective / directional detection method can be used in such cases, but they cannot be implemented without voltage measurements. If the radial connected feeders are grounded via resistor at neutral point on busbar,...
The performance of the negative sequence pilot protection (NSPP) is less deteriorated by the phase-ground shunt capacitance since the negative sequence current loops in phase-phase lines. Hence NSPP is a good candidate for the main protection in UHV lines with the special characteristic of larger charging current. But as we all known, NSPP is not suit to the open-phase operations in transmission line,...
Utilizing information of the wide area phasor measurement units (PMU), a novel self-adaptive fault-component based distance protection scheme is proposed. It aims at removing the defects of the conventional fault-component based distance relay. This scheme can adjust the operation threshold dynamically, depending on the real-time parameter measurement of two equivalent power systems. The limitations...
Under the conditions of the various system parameters and fault types, the performance of the phase selector based on modular fault component are analyzed. Compared with the phase selector based on difference of two phase currents, this phase selector is better in terms of overall performance. However, this phase selector cannot achieve theoretical selectivity for a real fault. Furthermore, this phase...
The performance of two types of current differential protection criteria is investigated by quantitative analysis. Among which, one is the criterion based on phase current differential (PD), and the other is implemented based on the phase-phase current differential (PPD). Some manufacturers claim that the zero sequence current is removed when PPD based criterion is applied and the sensitivity of the...
A sensor of electronic voltage transformer (EVT) was designed for the purpose of measurement in the medium/low voltage grids. Among which, a metal electrode was fixed into the center of a polytetrafluoroethylene (PTFE) cylinder, and stuck a double-sided flexible printed circuit board (FPCB) on the cylinder surface. With this arrangement, the metal electrode, the PTFE cylinder and the double-sided...
In a neutral non-effectively grounded power system, the correct identification and isolation of the faulty feeder on the occurrence of a single-phase earth fault is always a difficult task. To improve the level of distribution automation, a novel method of negative-sequence current compensation based adaptive zero-sequence over-voltage protection is put forward in this paper. On the basis of the analysis...
To correctly apply transformer differential protection in the environment of UHV (ultra high voltage), it is necessary to model the UHV power transformer reasonably and carry out corresponding electromagnetic transient simulations. Therefore, according to the equivalent circuit of three winding auto-transformer, we firstly set up the three winding autotransformer model by means of UMEC (Unified Magnetic...
The paper presents a novel feeder automation system based on non-communication protection and control unit (PCU) without the need of communication. The system can be adaptive to the changes of distribution network configuration. As a fault occurs on a feeder, Non-Communication Protection at the faulted segment's terminals will operate to isolate the faulted segment. The segments out of service will...
This paper main focus on the 3-D modulation scheme and neutral-point unbalance problem of 3-level 3-leg converter for active power filters. The neutral point unbalance problem is a key issue for this topology based APFs. To date there hasn't any perfect 3-D modulation solutions to tackle with neutral point unbalance problem well. In this paper, a detailed discussion on this issue is carried out. The...
Transformer is one of the most important elements in power system, but the correct operation percentage of protection relay is far less than that for line protection. Current differential protection has been the main protection technique for transformer unit. This protection technique, however, suffers a low sensitivity or reliability due to the problems such as CT saturation and transformer magnetizing...
The paper proposes the protection schemes for closed loop distribution network with distributed generators. Generally, Most of distribution networks are operated in radial or open loop due to the security and protection limited. With the rapid expansion of modern power systems and demand for high quality of power supply, the closed loop operation is adopted gradually. Furthermore, with the increasing...
Appropriate modeling of dynamic loads is of primary importance in voltage stability studies, especially increasing use of induction machines in both consumption and generation. This paper is mainly related to short-term voltage instability depending on time domain simulation. The actuality of voltage instability research is summarized, and the mechanisms of short- term voltage stability are explained...
This paper presents a new practical backup power supply connection scheme for distribution line non-communication protection (DNCP). Simulation tests have been conducted using the alternate transient program (ATP) with respect to a typical single circuit breaker multi-section system. The results prove that the new scheme is able to not only recover the power supply of loads on healthy lines automatically,...
Based on the frequency characteristics analysis, the selection criterion of lumped parameters circuits are presented in this paper. Firstly the Γ section equivalent circuit is introduced as the equivalent of transmission line and its validity is proved. With other lumped parameters circuits, their frequency characteristics are analyzed and compared with the distributed parameters circuit. From characteristic...
The impedance algorithm in distance protection for high voltage (HV) and extra high voltage (EHV) lines, although neglecting the influence of shunt capacitance, is able to produce satisfactory performance. However, the accuracy of the algorithm is significantly reduced when applying to ultra high voltage (UHV) lines due to the larger P.U. line shunt capacitance and longer transmission radius. Therefore,...
This paper presents an integrated PMU and protection scheme for power systems. The scheme integrates local and wide area control and protection systems by implementing the WAMS function and substation protections into one system to identify the overload caused by flow transfer from isolation of main trunk line. This integrated system mainly consists of three major components: local interface unit...
The paper studies distribution network with comprehensive micro-grid systems with an aim to design an advanced protection and control scheme. The proposed integrated protection and control (IPC) unit, interfacing to the substation measurement devices and micro-grid components through a substation optical Ethernet, is responsible for the protection of the distribution substation and control of its...
A back-up protection scheme for a distribution network is described in the paper. The progresses in microprocessor, communication and transducer technologies have provided new means for the design and development of new generation of algorithms and devices in power system. Studies have found that the fault generated electric quantities can not only be detected by integrated relay to achieve the line...
Modeling study provides a more effective and flexible way for research of high impedance fault (HIF) detection. An accurate model which can reveal most features of HIF is very important. In this paper, based on extensive investigation into documented test results, a set of most common and agreeable features of HIF has been summarized: the arc features, the non-linearity, the time-varied resistance...
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