Multi-grounded Neutral Research Articles

A New Method to Monitor the Primary Neutral Integrity in Multi-Grounded Neutral Systems

In the three-phase four-wire system, there are usually multiple grounding points in the primary neutral line due to safety and economic considerations. The rising “neutral to earth voltage (NEV)” caused by a broken primary neutral can threaten the safety of nearby facilities and humans; therefore, the integrity of the primary neutral conductor is of vital importance for the multi-grounded neutral (MGN) system. In this paper, a new passive method is proposed to monitor the integrity of the primary neutral line in the MGN system. The method is based on the measured voltage and current data at the service transformer, and there is no need to install any signal generators. Therefore, it causes no disturbance to the utility and customer. In the paper, the equivalent analysis circuit is established and a new parameter is proposed to reflect the neutral condition. The value of the parameter is estimated based on the measured data, and then, the equivalent impedance of the primary neutral groundings can be obtained. On the other hand, the impedance value for the primary neutral under normal operating conditions can be estimated based on the derived analytical formulas. By comparing the monitored primary neutral impedance with its normal value, the broken neutral condition in the primary system can be detected. Different primary neutral broken cases are analyzed in the paper based on the Monte Carlo simulation. The results indicate that the integrity condition in the primary neutral can be accurately monitored by the proposed method.

Shielding effect of multi-grounded neutral wire in the distribution system

The voltage induced by the power line on the nearby conductors, like telephone lines and pipelines, is investigated in this paper. The relationship between the phase currents and the neutral current plays an important role in reducing the induced voltage. Firstly, the impact of the MGN (multi-grounded neutral) configurations on the induced voltage is analyzed. It is found that the MGN-I (Islanded MGN) is the most practical configuration to reduce the induced voltage. Then a new method to calculate the neutral current for MGN-I is proposed. Based on the proposed method, a series of charts for neutral wire selections are given to facilitate the field engineers select the proper neutral wire. Finally, the validation of the proposed method is verified by the results obtained from EMTP-based multiphase harmonic load flow (MHLF) program. Copyright © 2010 John Wiley & Sons, Ltd.

Temporary Overvoltage and GPR Characteristics of Distribution Feeders With Multigrounded Neutral

Three-phase four-wire multigrounded neutral (MGN) is the preferred distribution line configuration in North America. Its performance characteristics, such as temporary overvoltage (voltage swell) and ground potential rise (GPR), are difficult to understand and assess due to the presence of a neutral conductor and the conductor's multiple grounding nature. The characteristics are further affected by unique parameters, such as grounding intervals and the coupling between neutral and phase conductors. This paper conducts analytical studies on the phenomena of temporary overvoltage and GPR associated with MGN configurations. The purpose is to reveal the mechanisms leading to the phenomena and their contributing factors. Approximate formulae are derived to quantify the impact of various factors. The findings are confirmed by the simulation results.

CHARACTERISTICS OF VOLTAGE IMBALANCE AND NEUTRAL CURRENT AND VOLTAGE DISTRIBUTIONS IN MULTI-GROUNDED SYSTEMS

The multi-grounded neutral (MGN) distribution lines are the most common means of power delivery in North America. Unbalanced customer loads can create significant voltage imbalances, leading to severe consequences, including equipment malfunction. Different configurations of the neutral conductor in MGN schemes can alter system performance. The neutral voltage associated with MGN systems is the safety concern. This paper presents the voltage imbalance characteristics of an MGN system under unbalanced load conditions, and for a variety of MGN layouts. The study also identifies the parameters that significantly impact the voltage imbalance. Although the main focus of this study is the voltage imbalance, the currents and voltages of the neutral conductor are also illustrated. A Multiphase Harmonic Load Flow (MHLF) program was used in this study. The results in this paper will help enhance the understanding of the performance of MGN systems.

Characteristics of Voltage Swell in Multigrounded Systems

The effects of multigrounded neutral (MGN) in three-phase distribution systems are not easy to analyze due to the presence of a fourth conductor-the neutral and its multigrounded arrangement. As a result, the mechanism of voltage swell in MGN feeders becomes difficult to understand. The amount of voltage swell in a MGN feeder is affected by unique factors such as the current in the neutral wire and the neutral-to-phase voltage induction. The purpose of this letter is to reveal and quantify all factors that contribute to voltage swell and substation ground potential rise in an MGN system. The results are expected to help utility engineers to understand the impact of MGN on distribution system operations and to assist their deployment of the MGN schemes

Contact current hypothesis: Summary of results to date

Research conducted over the past 5 years has addressed the hypothesis that the reported association between residential magnetic fields and childhood leukemia may be explained by exposure to contact current. The use of multi-grounded neutrals in electrical distribution and residential electrical wiring systems in the United States results in a voltage on a residence's water line relative to earth that in turn creates a voltage between the water fixtures of a bathtub, sink, or shower and the drain, if the latter is made of conductive material. A bathing child may thus be exposed to contact current upon manual contact with the faucet, spout, or water stream. Dosimetry modeling indicates that modest and realistically anticipated currents (10s of microA) can produce electric fields in bone marrow (100s of mV/m) sufficient to overcome questions of biophysical plausibility. Both measurements in two regions of the United States and computer modeling of typical single-residence US neighborhoods indicate that residences with average magnetic fields in the high tail of the magnetic field distribution are more likely than residences with lower fields to also have higher contact voltage. The association of residential magnetic fields with contact voltage, the dosimetry results, and the indication from a behavioral survey that children tend to engage in behavior that results in exposure all support the hypothesis. Further research is needed to characterize electrical systems in other nations to determine whether contact current exposure occurs and whether it is associated with residential magnetic fields.

Impedance of multigrounded neutrals on rural distribution systems

Hydro-Quebec has conducted field tests to study the impedance of multigrounded neutrals on rural distribution systems. Phase-to-neutral faults were staged at different locations along a 25 kV line and the field test results are reported. A simplified computer model implemented on EMTP gives results very close to those yielded by field tests. The main conclusion is that customers' grounding systems determine the impedance of multigrounded neutrals. Test results also show that the current is shared more or less equally between the neutral conductor and the sheaths of CATV and telephone cables. Overvoltages on phase conductors during phase-to-neutral faults were also measured and results are presented. >

Calculation of Unbalanced voltage Drops in Distribution Circuits With Particular Reference to Multigrounded Neutrals

Calculation of Unbalanced voltage Drops in Distribution Circuits With Particular Reference to Multigrounded Neutrals

Transactions section: Calculation of unbalanced voltage drops in distribution circuits with particular reference to multi-grounded neutrals

Transactions section: Calculation of unbalanced voltage drops in distribution circuits with particular reference to multi-grounded neutrals