Power Factor Explained - The basics what is power factor pf — Transcript

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1. 0:04Hey there guys.
2. 0:05Paul here from TheEngineeringMindset.com
3. 0:07In this video, we're going to be discussing
4. 0:09power factor, we're going to start off really
5. 0:12easily with some simple analogies
6. 0:13to help you understand the basics, and then
7. 0:15we'll advance it into electrical
8. 0:17engineering terms with some work examples
9. 0:19as well as looking at what is power factor,
10. 0:21what is a good and bad power factor,
11. 0:24what causes bad power factor,
12. 0:26and how to fix bad power factor.
13. 0:28So what is power factor?
14. 0:30Power factor is a unitless number
15. 0:32using alternating current circuits.
16. 0:34It can be used to refer to a single piece of
17. 0:36equipment such as an induction motor or through
18. 0:39electricity consumption of an entire building.
19. 0:42In either case, it represents the ratio between
20. 0:44true power and apparent power.
21. 0:46The formula being PF equals KW divided by kVa.
22. 0:50So what does that mean?
23. 0:52My favourite analogy to explain this
24. 0:54is to use the beer analogy.
25. 0:56We pay for beer by the glass, but inside the glass
26. 0:59there is both beer and foam.
27. 1:01The more beer we have, the less foam there will be, so
28. 1:03we get very good value for money.
29. 1:05If there is a lot of foam, then there's not a lot of beer,
30. 1:08and so we're not getting very good value for money.
31. 1:10The beer represents our true power or kW, our kilowatts.
32. 1:14This is the useful stuff you want and need.
33. 1:16This is what does the work.
34. 1:18The foam represents our reactive power, or our
35. 1:20kVar, Kilovolt-Amps Reactives.
36. 1:24This is the useless stuff, there will always
37. 1:26be some, we have to pay for it, we can't use it
38. 1:28so we don't really want much of it.
39. 1:30It does actually have a use and a purpose,
40. 1:33but we'll see why later in the video.
41. 1:35The combination of these kW are kilowatts
42. 1:38and the kVar are Kilovolts-Amp Reactive,
43. 1:41is our apparent power or our kVA, meaning
44. 1:44the kilovolt amps.
45. 1:45Power factor is therefore
46. 1:46the ratio of useful power or true power
47. 1:50in kilowatts, or kW divided by what we're
48. 1:52charged for in kVA, kilovolt-amps.
49. 1:55So it's telling us how much value for money
50. 1:58we're getting for the power we consume.
51. 2:00If we briefly touch on electrical engineering,
52. 2:03and I will keep this part brief, then we might
53. 2:05see this express as a power triangle.
54. 2:07In this case I'll draw it as leading
55. 2:09power factor as it's easier to visualize.
56. 2:12The beer or true power is the adjacent line.
57. 2:15Then we have the foam which is the reactive
58. 2:16power on the opposite.
59. 2:18Then for the hypotenuse side, which is the
60. 2:20longest side, we have the apparent power.
61. 2:23This is at an angle from the true power, the
62. 2:25angle is known as theta.
63. 2:26You see as the reactive power or the foam
64. 2:29increases then so does the apparent power
65. 2:31of the kVA.
66. 2:33WE could then use trigonometry
67. 2:34to calculate this triangle.
68. 2:35I won't in this video as I'm just covering the basics,
69. 2:38so we'll just see the formulas you need,
70. 2:40but we'll do some calculations
71. 2:41and worked examples later in this video.
72. 2:44If we look at a typical residential
73. 2:46electricity bill, then we'll typically see
74. 2:48just a fee for the amount of kilowatts
75. 2:49hours used, because the power factor
76. 2:51and the electricity consumption will
77. 2:53be very low.
78. 2:54So the electricity companies
79. 2:55tend to not worry about this.
80. 2:57However on commercial and industrial electricity invoices,
81. 3:00especially buildings with smart
82. 3:02or interval electricity meters, then we'll
83. 3:04likely see charges and information
84. 3:06for the amount of kilowatts, kilowatt hours,
85. 3:08kilovolt amps, and kilovolts-amps reactive used.
86. 3:11Large buildings in particular will often
87. 3:13see reactive power charges in there.
88. 3:15But this depends on the electricity supplier,
89. 3:17and the agreement they have with the consumer.
90. 3:19They reason they charge a penalty for this
91. 3:21is because when large consumers have bad
92. 3:23power factors, they're increasing
93. 3:25the current flow through
94. 3:26the electricity network, and causing voltage drops,
95. 3:29which reduces the supplier's distribution
96. 3:31capacity and has a knock on effect
97. 3:34for the other customers.
98. 3:35Cable are rated to handle
99. 3:38a certain amount of current flowing for them.
100. 3:39So if a lot of large consumers connect
101. 3:41with bad power factor, then the cables could overload.
102. 3:45It could also struggle
103. 3:46to meet the demands and the capacity agreements,
104. 3:48and then no new customers will be able
105. 3:49to connect, until they either replace the cables,
106. 3:52or install additional cables.
107. 3:54Reactive power charges occur when the
108. 3:56power factor of a building falls below
109. 3:58a certain level.
110. 3:59This level is defined by
111. 4:01the electricity supplier, but it typically
112. 4:03starts around 0.95 and below.
113. 4:06A perfect power factor would be one, however
114. 4:08in reality, this is almost impossible to achieve.
115. 4:11We'll come back to this part
116. 4:12later in the video.
117. 4:14In large commercial buildings, the overall
118. 4:16power factor is likely to sit
119. 4:18in the following categories.
120. 4:19Good power factor is generally between one and 0.95
121. 4:24Poor power factor is anything from 0.95 and 0.85.
122. 4:28Bad power factor is anything below 0.85.
123. 4:32Commercial office buildings are usually somewhere
124. 4:34between 0.98 and 0.92.
125. 4:37Industrial buildings could be as low as 0.7.
126. 4:40We'll look out what causes this shortly.
127. 4:43Let's first have a look at an example.
128. 4:46If we compare two induction motors, that
129. 4:49both have an output of 10 kilowatts, and are
130. 4:51connected to a three phase 415/50 hertz supplier,
131. 4:54one has a power factor of 0.87, and the other
132. 4:58with the power factor of 0.92.
133. 5:00Both motors will deliver 10 kilowatts of work,
134. 5:03but the first motor has a lower power factor
135. 5:05compared to the second one.
136. 5:07Meaning we're not getting as much value for money.
137. 5:10The first motor will need to draw
138. 5:1111.5 kVA from the electricity grid to provide
139. 5:15the 10 kilowatts of power, the second motor
140. 5:18will need to draw just 10.9 kVA from
141. 5:20the electricity grid to provide
142. 5:22the same 10 kilowatts of power.
143. 5:23This means the first motor has 5.7kVAr
144. 5:27and the second motor has just 4.3kVArs
145. 5:30Remember our kilowatts is the beer,
146. 5:32and that's the useful stuff.
147. 5:33The kVArs are the foam, that's the not so useful stuff.
148. 5:36The kVA is what we're going to pay for,
149. 5:39and that's the kilowatts and the kVAr combined.
150. 5:42How did I calculate that?
151. 5:43For kVA I use kilowatts divided by power factor
152. 5:46so 10 divided by 0.87 to get 11.5 kVa.
153. 5:51For kVAr I use the square root of kVA squared,
154. 5:54subtract kilowatts squared.
155. 5:56So the square root
156. 5:57of 11.5 kVA squared minus 10 kilowatts squared.
157. 6:00We could've also found the power factor
158. 6:02from the kilowatt and the kVA, using
159. 6:0410 kilowatt divided by 11.5 kVA.
160. 6:07We could've found the kilowatts from
161. 6:09the power factor and the kVA using 0.87
162. 6:12divided by 11.5 kVA to get 10.
163. 6:16So what causes poor power factor?
164. 6:18In most cases the power factor
165. 6:20is affected by inductive loads.
166. 6:23If we have a purely resistive load, such as
167. 6:25an electrical resistive heater, then the voltage
168. 6:27and the current wave forms would be in sync
169. 6:29or very close.
170. 6:31They would both pass through their maximum
171. 6:33and minimum point and then pass through
172. 6:35the zero axis at the same time.
173. 6:37The power factor in this case is one,
174. 6:39which is perfect.
175. 6:41If we drew a phaser diagram, then the voltage and
176. 6:43and current would be parallel.
177. 6:45So all the energy drawn from the electricity
178. 6:47supply goes into doing work.
179. 6:50In this case creating heat.
180. 6:53But if we took an inductive load, such as
181. 6:55an induction motor, then the coils
182. 6:57magnetic field holds back the current and results
183. 7:00in the phase shift where the voltage
184. 7:01and the current waveforms fall out of sync
185. 7:04with each other, so the current passes
186. 7:06through the zero point after the voltage.
187. 7:09This is referred to as a lagging power factor.
188. 7:12Earlier in the video,
189. 7:13I said the foam or the kVAr is useless.
190. 7:16That's not exactly true.
191. 7:18You actually need some reactive power to create
192. 7:20and maintain the magnetic field
193. 7:22which rotates the motor.
194. 7:24The reactive power is wasted in the sense
195. 7:26that we get no work from it.
196. 7:27But we still have to pay for it although we do need it
197. 7:30to be able to do the work in the first place.
198. 7:33If we drew a phaser diagram for a purely
199. 7:35inductive load, then the current would be at an
200. 7:37angle below the voltage line.
201. 7:39Meaning not all the electricity consumed is doing work.
202. 7:43If we took a purely capacitive load,
203. 7:45then the opposite happens
204. 7:46to the inductive load.
205. 7:48The voltage and current are out of phase, except
206. 7:50this time the voltage is held back.
207. 7:53This causes leading power factor.
208. 7:55Again this will mean that not all of the
209. 7:57electricity being used is being used to do work.
210. 8:00But we still have to pay for it regardless.
211. 8:03If we drew a phaser diagram for a
212. 8:04purely capacitive load, then the current line
213. 8:07will be at an angle above the voltage line,
214. 8:09as it's leading.
215. 8:12Correcting poor power factor.
216. 8:14What can we do to correct poor power factor
217. 8:17and reactive power charges?
218. 8:19In most case we come across lagging power factor
219. 8:21caused by inductive loads.
220. 8:23To correct poor power
221. 8:24factor, we can add capacitors or inductors to
222. 8:27the circuit, which will realign the current back
223. 8:29into phase and bring the power factor
224. 8:31closer to one.
225. 8:32If we have a lagging power factor, caused by
226. 8:34high inductive loads in the circuit,
227. 8:36then we add capacitors.
228. 8:38If we have a leading power
229. 8:39factor, caused by high capacitive loads, then we
230. 8:42add an inductive load to the circuit.
231. 8:44These need to be calculated, and we'll see
232. 8:46some example calculations of this
233. 8:47at the end of the video.
234. 8:49So why should we fix poor power factor?
235. 8:51Poor power factor means you need to draw more
236. 8:53power from the electricity network
237. 8:55to do the same amount of work, therefore
238. 8:57the cables need to be larger so the installation
239. 9:00is going to cost more money.
240. 9:01If the power factor becomes too low,
241. 9:03then the electricity supplier might charge you
242. 9:05a penalty fee or reactive power charge.
243. 9:08Poor power factor can cause losses
244. 9:10in the equipment, like transformers,
245. 9:11and leads to high heat gains.
246. 9:13It can lead to voltage drops and can even reduce
247. 9:15the life expectancy of equipment
248. 9:17in extreme scenarios.
249. 9:19Capacitor calculations for power factor correction.
250. 9:23Let's look at a simplified example of calculating
251. 9:26the size of a capacitor to improve
252. 9:27the power factor of a load.
253. 9:30The building has a three phase power supply
254. 9:32and has a total load of 50 kilowatts of work.
255. 9:35It also has a power factor of 0.78, but we
256. 9:38want it to be 0.96 to avoid penalty charges.
257. 9:42Currently the building has a total apparent power
258. 9:44or kVA value of 64.1 kVA and we find that
259. 9:49by just dividing the kilowatts, 50 kilowatts
260. 9:52by the power factor of 0.78.
261. 9:54It also has a reactive power of 40.1 kVAr.
262. 9:58We find that by taking the square root of the
263. 10:00kVA squared and subtracting it from
264. 10:03the kilowatts squared.
265. 10:04So take the squared root
266. 10:06of 64.1 squared minus 50 kilowatts squared.
267. 10:09Then we calculate what the value should be
268. 10:11if we had a power factor of 0.96.
269. 10:14SO our apparent power should be 52.1 kVA.
270. 10:18We find that from 50 kilowatts divided by
271. 10:210.96 power factor.
272. 10:23Then we find our reactive power which is
273. 10:25the square root of the kVA squared
274. 10:27minus the kilowatts squared.
275. 10:29So the square root
276. 10:30of 52.1 kVA squared minus 50 kilowatts squared
277. 10:34which gives us 14.6 kVAr.
278. 10:37The capacitor therefore
279. 10:38needs to make up the difference between these.
280. 10:40So 40.1 kVAr minus 14.6 kVAr which equals
281. 10:45a 25.5 kVAr capacitor.
282. 10:48Okay guys, that's it for this video,
283. 10:50but if you want to continue your learning,
284. 10:52check out these videos here.
285. 10:53I'll catch you there for the next lesson.
286. 10:55Leave you questions in
287. 10:56the comments section down below, and don't forget
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289. 11:00as well as TheEngineeringmindset.com.