41:
205:
50:
325:
313:
301:
28:
20:
251:
tubes, insulating columns often have many metal grading rings spaced evenly along their length. These are linked by a voltage divider chain of high-value resistors so there is an equal voltage drop from each ring to the next. This divides the potential difference evenly along the length of the column
184:
of air. It is roughly 30 kV/cm at sea level but decreases when atmospheric pressure decreases. Therefore, corona discharge is more of a problem at high altitudes. The electric field at the surface of a conductor is greatest where the curvature is sharpest, so corona discharge occurs first at sharp
235:
and become conductive at that end first. Once a section of the insulator at the end has electrically broken down and become conductive, the full voltage is applied across the remaining length, so the breakdown will quickly progress from the high voltage end to the other, and a flashover arc will
195:
The corona ring is electrically connected to the high voltage conductor, encircling the points where corona would form. Since the ring is at the same potential as the conductor, the presence of the ring reduces the potential gradient at the surface of the conductor below the disruptive potential
276:
insulators, bushings, and switchgear. Manufacturers suggest a corona ring on the line end of the insulator for transmission lines above 230 kV and on both ends for potentials above 500 kV. Corona rings prolong the lifetime of insulator surfaces by suppressing the effects of corona
239:
The grading ring surrounds the end of the insulator next to the high voltage conductor. It reduces the gradient at the end, resulting in a more even voltage gradient along the insulator, allowing a shorter, cheaper insulator to be used for a given voltage. Grading rings also reduce aging and
192:, to suppress corona formation. Some parts of high voltage circuits have hardware with exposed sharp edges or corners, such as the attachment points where wires or bus bars are connected to insulators; corona caps and rings are usually installed at these points to prevent corona formation.
224:, is also used on high-voltage equipment. Grading rings are similar to corona rings, but they encircle insulators rather than conductors. Although they may also serve to suppress corona, their main purpose is to reduce the potential gradient along the insulator, preventing premature
163:
gas, which can cause aging and brittleness of nearby structures such as insulators. The gasses create a health hazard for workers and local residents. For these reasons corona discharge is considered undesirable in most electrical equipment.
151:. In very high voltage electric power transmission lines and equipment, corona results in an economically significant waste of power and may deteriorate the hardware from its original state. In devices such as
231:
The potential gradient (electric field) across an insulator is not uniform but is highest at the end next to the high voltage electrode. If subjected to a high enough voltage, the insulator will
140:
is a leakage of electric current into the air adjacent to high voltage conductors. It is sometimes visible as a dim blue glow in the air next to sharp points on high voltage equipment. The high
159:, and tube-type television sets, the current load caused by corona leakage can reduce the voltage produced by the device, causing it to malfunction. Coronas also produce noxious and corrosive
451:
188:
The terminals on very high voltage equipment are frequently designed with large diameter rounded shapes such as balls and toruses called
236:
start. Therefore, insulators can stand significantly higher voltages if the potential gradient at the high voltage end is reduced.
389:
370:
265:
70:
40:
362:
441:
426:
381:
400:
421:
273:
112:
204:
213:
261:
240:
deterioration of the insulator that can occur at the high voltage end due to the high electric field there.
152:
104:
80:
119:, and on scientific research apparatus that generates high voltages. A very similar related device, the
147:
the air, making it conductive, allowing current to leak from the conductor into the air in the form of
49:
446:
269:
248:
232:
225:
96:
177:
62:
209:
324:
385:
366:
285:
92:
312:
137:
132:
108:
27:
281:
244:
173:
156:
141:
99:, usually metal, which is attached to a terminal or other irregular hardware piece of
435:
343:
300:
252:
so there are no high field spots, resulting in the least stress on the insulators.
100:
19:
289:
176:(potential gradient) at the surface of conductors exceeds a critical value, the
144:
116:
31:
Corona rings on insulator strings on a 225 kV transmission line in France
416:
107:
and lower its maximum values below the corona threshold, preventing
363:
Electric power generation, transmission, and distribution, Volume 1
203:
160:
26:
23:
Corona discharge on insulator string of a 500 kV transmission line
18:
260:
Corona rings are used on extremely high voltage apparatus like
103:
equipment. The purpose of the corona ring is to distribute the
196:
gradient, preventing corona from forming on the metal points.
148:
16:
Device preventing corona discharge on high voltage equipment
280:
Corona rings may also be installed on the insulators of
427:Differences Between Corona Rings And Grading Rings
61:Grading rings on 1.4 MV X-ray generator at the US
111:. Corona rings are used on very high voltage
73:from 1937, now in the Science Museum, London.
8:
401:aerials for metre and decimetre wave-lengths
382:The Handbook of antenna design, Volume 2
365:By Leonard L. Grigsby, CRC Press, 2007,
306:Grading ring on a Russian surge arrester
220:A very similar related device, called a
355:
172:Corona discharges only occur when the
384:By Alan W. Rudge, IET, 1983, p. 873,
318:Grading rings on transformer bushings
71:Cockcroft–Walton particle accelerator
7:
243:In very high voltage apparatus like
87:, more correctly referred to as an
14:
452:Electric power systems components
323:
311:
299:
48:
39:
1:
288:. However, they increase the
182:disruptive potential gradient
123:, is used around insulators.
69:Corona caps and rings on the
330:Corona rings on switch gear
274:electric power transmission
266:Cockcroft–Walton generators
185:points, corners and edges.
468:
214:University of Pennsylvania
130:
262:Van de Graaff generators
153:electrostatic generators
105:electric field gradient
217:
208:Grading rings along a
81:electrical engineering
32:
24:
270:particle accelerators
207:
30:
22:
442:Electrical breakdown
422:What is Grading Ring
249:particle accelerator
226:electrical breakdown
292:of the insulators.
178:dielectric strength
97:conductive material
63:Bureau of Standards
286:radio transmitters
218:
210:linear accelerator
113:power transmission
33:
25:
417:Highv Corona Ring
212:beam tube at the
459:
404:
398:
392:
379:
373:
360:
327:
315:
303:
138:Corona discharge
133:Corona discharge
127:Corona discharge
109:corona discharge
89:anti-corona ring
52:
43:
467:
466:
462:
461:
460:
458:
457:
456:
432:
431:
413:
408:
407:
399:
395:
380:
376:
361:
357:
352:
340:
335:
334:
333:
332:
331:
328:
320:
319:
316:
308:
307:
304:
258:
245:Marx generators
202:
170:
157:Marx generators
135:
129:
115:insulators and
77:
76:
75:
74:
55:
54:
53:
45:
44:
17:
12:
11:
5:
465:
463:
455:
454:
449:
444:
434:
433:
430:
429:
424:
419:
412:
411:External links
409:
406:
405:
393:
374:
354:
353:
351:
348:
347:
346:
339:
336:
329:
322:
321:
317:
310:
309:
305:
298:
297:
296:
295:
294:
284:of high-power
257:
254:
201:
198:
174:electric field
169:
166:
142:electric field
131:Main article:
128:
125:
57:
56:
47:
46:
38:
37:
36:
35:
34:
15:
13:
10:
9:
6:
4:
3:
2:
464:
453:
450:
448:
445:
443:
440:
439:
437:
428:
425:
423:
420:
418:
415:
414:
410:
403:, CUP Archive
402:
397:
394:
391:
390:0-906048-87-7
387:
383:
378:
375:
372:
371:0-8493-9292-6
368:
364:
359:
356:
349:
345:
342:
341:
337:
326:
314:
302:
293:
291:
287:
283:
278:
275:
272:, as well as
271:
267:
263:
255:
253:
250:
246:
241:
237:
234:
229:
227:
223:
215:
211:
206:
200:Grading rings
199:
197:
193:
191:
186:
183:
179:
175:
168:How they work
167:
165:
162:
158:
154:
150:
146:
143:
139:
134:
126:
124:
122:
118:
114:
110:
106:
102:
98:
94:
90:
86:
82:
72:
68:
64:
60:
51:
42:
29:
21:
396:
377:
358:
344:Arcing horns
279:
259:
242:
238:
230:
222:grading ring
221:
219:
194:
189:
187:
181:
171:
136:
121:grading ring
120:
101:high voltage
88:
84:
78:
66:
58:
447:Dielectrics
290:capacitance
277:discharge.
190:corona caps
85:corona ring
436:Categories
350:References
233:break down
117:switchgear
65:in 1947.
338:See also
282:antennas
216:in 1940
145:ionizes
91:, is a
67:(right)
388:
369:
268:, and
93:toroid
59:(left)
228:.
161:ozone
386:ISBN
367:ISBN
256:Uses
247:and
149:ions
83:, a
264:,
180:or
95:of
79:In
438::
155:,
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
