Peter E. Sutherland

Harmonic measurements in industrial power systems

Harmonic measurements are made in industrial power systems in order to: (a) aid in the design of capacitor or filter banks; (b) verify the design and installation of capacitor or filter banks; (c) verify compliance with utility harmonic distortion requirements; and (d) investigate suspected harmonic problems. The results of these measurements are used in design calculations, verification, comparison with standards, and system modeling. Each of these objectives will affect the choice of a measurement approach. The selection of the measured quantities, measurement points in the system, and the types of instruments and transducers should be based upon the measurement objective. Once measurements are taken, additional calculations must be made to put the results into a useful form. The measurement results will then provide a firm basis for further engineering work.<<ETX>>Harmonic measurements are made in industrial power systems in order to: (a) aid in the design of capacitor or filter banks, (b) verify the design and installation of capacitor or filter banks, (c) verify compliance with utility harmonic distortion requirements, and (d) investigate suspected harmonic problems. The results of these measurements are used in design calculations, verification, comparison with standards, and system modeling. Each of these objectives will affect the choice of a measurement approach. The selection of the measured quantities, measurement points in the system, and the types of instruments and transducers should be based upon the measurement objective. Once measurements are taken, additional calculations must be made to put the results into a useful form. The measurement results will then provide a firm basis for further engineering work.

Electrical safety for employee workplaces in Europe and in the USA

The USA and Europe use different standards to provide electrical safety for employee workplaces. This paper examines the two standards NFPA70E and EN 50110, shows some of the similarities and differences, and looks at the possibilities for a gradual harmonization between the two systems. The paper would contribute to improve the electrical safety continuity in the worldwide globalization efforts.

Optimized Instantaneous Protection Settings: Improving Selectivity and Arc-Flash Protection

In todays power distribution systems, the protection methods do not provide full selectivity and instantaneous fault clearing for expected fault current, including lower-magnitude arcing currents simultaneously. This article discusses two methods that may change that. The first method is a selectivity analytical technique useful with many circuit breaker (CB) trips currently available in the industry. The second method is a new CB trip technology. Both methods allow switch gear CBs to use sensitive instantaneous settings and maintain selectivity when used in upstream current-limiting (CL) molded case CBs (MCCBs), CL motor circuit protectors (MCPs), or CL fuses in downstream equipment such as motor control centers (MCCs).

DC short-circuit analysis for systems with static sources

When calculating available fault currents for DC systems with static converters as sources, the internal resistance of the source must be adjusted based upon the terminal voltage of the source. If the system has a single source, an iterative technique is normally used. However, this becomes cumbersome when solving systems with multiple sources and multiple fault locations. Previous methods have adjusted the resistance of all static sources by a fixed percentage. Methods for providing multiplying factors to adjust the fault contributions of static sources which differentiates between local and remote sources are discussed. Individual multiplying factors for each source may be calculated by means of a formula, or an approximate multiplying factor for all sources may be found by iteration. The multiplying factors are then applied to the results of a single step matrix solution for the short-circuit currents. This facilitates the use of computer spreadsheet programs for the solution of the problem. It is concluded that the use of a fixed multiplying factor may offer the most conservative solution method.

Ensuring Stable Operation with Grid Codes: A Look at Canadian Wind Farm Interconnections

This article discusses windfarm electrical power system issues in grid codes. Grid codes are published by utilities and system operators to define the requirements for the interconnection of generation and other facilities to the grid. The purpose of the grid code requirements is to ensure reliability, stability, power quality, protection of equipment, and worker safety. These requirements are given at the point of interconnection (POI) with the transmission or distribution system and are different depending on the sizes and types of generation. Grid codes can cover a broad range of requirements, from continuous operational constraints to behavior during contingencies such as faults, and they vary considerably based on the issuer, their country or region, and the type of transmission or distribution system. Manufacturer specifications for wind turbines are generally given on a per-turbine basis at the collector system voltage. When a wind farm is proposed, an initial assessment is made of the suitability of the wind turbines to the system. Studies that evaluate system performance and conformance with the grid code are performed of the grid and wind farm(s) being considered. Finally, tests and measurements during and after commissioning verify conformance of the wind farm to the applicable grid code.

History of Harmonics [History]

Harmonics have been a concern in electric power systems since the beginnings of the electrical age. Harmonics are defined by IEEE Standard 519-2014 [1] as follows.

Modeling of impedance vs. frequency in harmonics analysis programs

Recently reported results give measurements of the resistance and inductance of power cables and transformers vs. frequency. In harmonics analysis computer programs, various methods, including linear and exponential approximations and eddy current factors are used to model the increase of resistance with frequency, while the inductance is assumed to be constant. The measured results from the paper of Rhode, Kelley and Saran (1996) are used in this paper to evaluate the accuracy of various models.

Performance calculation for tunnel boring machine motors

The performance of a tunnel boring machine (TBM) is dependent upon the mine power distribution system providing adequate voltage. The voltage at the motors may be calculated using a standard computer load flow program. These calculated voltages are compared to measured voltages in the tunnel. The classical induction motor equivalent circuit is used to calculate the torque output for a given voltage input. Current and speed versus horsepower curves are developed from the model and compared with motor test data. The motor modeling results are used to adjust the simplified motor model in the load flow program. The results of the calculation are a torque versus distance curve that summarizes the performance of the TBM. Using this method, the effects of changes in source voltage, transformer taps, cable size and other factors on machine performance can be evaluated.

Inductance Effects in Grounding and Bonding for Three-Phase AC Systems

Equipment grounding and bonding is important for electrical safety, in protecting against unwanted voltage and current, which can cause injury. The configurations of grounding and bonding conductors can be broken down into a number of typical arrangements. Inductance is an important factor in calculating the magnitude of ground fault currents. This paper examines and compares inductance formulas from the literature for a variety of grounding conductor configurations and return paths. It is found that the use of more accurate formulas than are normally used can present a significant improvement in the calculation of these inductances.

Current transformer application with digital ground differential protection relays

Ground differential protection relays (device 87G) have been used to protect the windings of resistance grounded power transformers. There have been problems of relay misoperation and nonoperation with electromechanical 87G relays due to current transformer (CT) burden and saturation. Due to their low burden, it has been assumed by some that solid-state digital relays are not subject to these problems. The purpose of this paper is to evaluate the truth of this assumption. Under what circumstances, and with what types of CTs, might problems occur? An analysis is performed of digital ground differential protection over a range of power transformer and CT sizes. Guidelines are developed for CT accuracy ratings suitable for this application. The effect of different relay algorithms on scheme performance relative to CTs is also discussed.