Edward Beck

Effects of Lightning Voltages on Rotating Machines and Methods of Protecting Against Them

Rotating machines directly connected to overhead lines are subject to damage from lightning surges. Many methods of protection against such damage are possible, several of which are discussed in this paper. Laboratory experiments have been made to show the normal distribution under various steepnesses of waves, and the improvement of unsatisfactory distributions by means of condensers or lightning arresters connected to various parts of the windings has been studied.

Lightning Protection for Rotating Machines

FIGURE 1 lists the valve-type machine-arrester and capacitor ratings recommended for each voltage class of machine together with their method of application. It is important that the arresters at the machine be valve type. They always should be applied with capacitors that are located either reasonably close to the arresters or between the arresters and machine. This combination prevents the occurrence of steep-front surges resulting from a sudden voltage drop when the arrester discharges.

Field Investigation of the Characteristics of Lightning Currents Discharged by Arresters

Data have been obtained during the past three years on the magnitude and wave shape of lightning currents discharged by arresters in service on several solidly grounded neutral circuits of the American Gas and Electric Company system. Correlated measurements have been obtained with the cathode-ray oscillograph, the fulchronograph, and the surge-front recorder. The maximum arrester-phase leg current recorded in this investigation was 9,600 amperes with 70 per cent of the currents less than 1,000 amperes. The wave fronts of the low-magnitude currents were, in general, abrupt. For crest magnitudes of over 1,000 amperes they ranged from two to over 25 microseconds to crest. The maximum rate of rise recorded was 2,500 amperes per microsecond.

Lightning and Lightning Protection on Distribution Systems

D. D. MacCarthy (General Electric Company, Pittsfield, Mass.): Messrs. Bergvall and Beck have presented an informative discussion of the division of long-duration lightning currents between arresters and the transformers connected to grounded-neutral circuits. This analysis confirms the prediction made by Doctor K. B. McEachron1 in February 1939 when he discussed some of the long-time discharges which he recorded oscillographically as early as 1937. In this article Doctor McEachron states, regarding continuing lightning discharges to grounded neutral systems: … the transformer winding represents a relatively small impedance to the flow of such unidirectional currents.

Symposium on Lightning Lightning on Transmission Lines Cathode Ray Oscillograph Studies

This paper is a review of the work done and results obtained in Norindertype cathode ray oscillograph studies of lightning on transmission lines during 1929. The various installations and methods of test are described. The wave shapes recorded are illustrated and their meaning discussed. The paper also contains a preliminary description of an artificial lightning investigation, using a portable 1,000,000-volt surge generator and a portable cathode ray oscillograph. The methods used and some of the preliminary results are discussed.

Dielectric Strength and Protection of Modern Dry-Type Air-Cooled Transformers

TODAY there are in service over 1,000,000 kva of large dry-type air-cooled transformers, some in ratings as high as 4,000 kva and including the 15-kv voltage class. This wide acceptance in industry of the modern dry-type transformer and its continual growth, naturally has increased interest in its application and standardization. In a prior AIEE paper1 the design characteristics, particularly with regard to thermal performance, have been discussed. The purpose of this paper is to review the development of the modern dry-type transformer, specifically with reference to its dielectric strength, and to present recommendations on impulse levels and methods of protection for applications which may be affected by lightning surges.

Protection of Supervisory Control Lines Against Over-Voltage

Supervisory control lines used in the remtote or automatic control of electric plants are subject to overvoltages dangerous to insulation and to operators. These overvoltages may be caused by lightning, crosses with the power lines, or induction from them. Open wire control lines are influenced by all of these, cables with grounded sheaths are immune to disturbances caused by lightning or other electrostatic induction, and are more or less safe from crosses. The ordinary cable, however, is still subject to high voltages by electromagnetic induction when a fault occurs on the power line. These voltages may be dangerous not only to apparatus, but also to the cable insulation. Protection by means of lightning arresters is therefore necessary. Calculationts show that even if the apparatus locations are protected, high voltages may occur along the line if the transmission line fault is between stations. This may cause a cable failure. It may, therefore, be advisable to protect the cable at certain intervals. Supervisory control protectors may be called upon to discharge heavy currents of appreciable duration. This requires extremely sturdy arresters. The requirements are met by a spark-gap of special design in argon at a reduced pressure. Specially made cables will shield the line against extraneous disturbances. In large installations, the use of such cables may be worthy of consideration.

Lightning Arresters for Distribution Apparatus

THERE are today two general types of lightning arresters in use for the protection of distribution apparatus. They are the valve type covered by AIEE Standard 28, and the expulsion type, for which AIEE Standards are being formulated. Both have been used widely for many years. Typical specimens are illustrated in Figure 1. The valve type is the older. The first distribution-valve arrester was an Autovalve produced in 1922. The first expulsion-type distribution arrester was the deion arrester (United States Patent, 2,050,397) used on surge-protected distribution transformers in 1931. By far the largest number of expulsion-type arresters manufactured have been applied as part of completely self-protected transformers. Many of these have used a somewhat different physical construction and mounting as shown in Figure 2 than that used for the arresters installed separately from the transformers. There exist today several variations of both the expulsion and valve types.

Abridgment of effects of lightning voltages on rotating machines and methods of protecting against them

Rotating machines directly connected to overhead lines are subject to damage from lightning surges. Many methods of protection against such damage are possible and several of them are discussed in this paper. Laboratory experiments have been made to show the normal distribution under various steepnesses of waves, and the improvement of unsatisfactory distributions by means of condensers or lightning arresters connected to various parts of the windings has been studied.

Abridgment of protection of supervisory control lines: Against over-voltage

Supervisory control lines used in the remote or automatic control of electric plants are subject to overvoltages dangerous to insulation and to operators. These overvoltages may be caused by lightning, crosses with the power lines, or induction from them. Open wire control lines are influenced by all of these, cables with grounded sheaths are immune to disturbances caused by lightning or other electrostatic induction, and are more or less safe from crosses. However, the ordinary cable is still subject to high voltages by electromagnetic induction when a fault occurs on the power line. These voltages may be dangerous not only to apparatus, but also to the cable insulation. Protection by means of lightning arresters is therefore necessary. Calculations show that even if the apparatus locations are protected, high voltages may occur along the line if the transmission line fault is between stations. This may cause a cable failure. It may, therefore, be advisable to protect the cable at certain intervals. Supervisory control protectors may be called upon to discharge heavy currents of appreciable duration. This requires extremely sturdy arresters. The requirements are met by a spark-gap of special design in argon at a reduced pressure. Specially made cables will shield the line against extraneous disturbances. In large installations, the use of such cables may be worthy of consideration.