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home | newest check | boards | help index | log | ps | userlogin | send sysop | slog | status forward | bcm news | users | version | remove cookieG8MNY > TECH 13.05.24 15:56l 134 Lines 6178 Bytes #8 (0) @ WW BID : 7625_GB7CIP Subj: AC 3 Phase Power Path: JH4XSY<JE7YGF<LU4ECL<I0OJJ<GB7CIP Sent: 240513/0645Z @:GB7CIP.#32.GBR.EURO #:7625 [Caterham Surrey GBR] $:7625_GB From: G8MNY@GB7CIP.#32.GBR.EURO To : TECH@WW By G8MNY (Updated Aug 08) (8 Bit ASCII graphics use code page 437 or 850, Terminal Font) 3 PHASE POWER This is how AC power is normally generated & distributed, it is more efficient than other AC systems, except for DC that is the most efficient, but that is difficult & costly to transform the voltage at high power. The wire colour scheme may differ between countries & also the voltage! The phase angle between phases is 120ø, because of this the voltages are added up vectorialy, so at first sight 2x 230V does not make 415V between 2 lives. You divide by û3 (1.732) to get the line to neutral voltage. Line BROWN ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ STAR LOADS DELTA LOADS (red) /³\ /³\ /³\ o Brown 415V | | Brown o \³/ 415V | Load / \ BLACK ÄÄÄÄÄÄÄÄÄÄÄÄÄ | ³ / 60ø \ (yellow) /³\ | /³\ | 120ø o 120ø 415V 415V 415V | | | / \ Load Load \³/ \³/ | | Grey 120ø Black / 60ø 60ø \ GREY ÄÄÄÄÄÄÄÄÄ | | Load Load o______ 415V ______o (blue) /³\ | | o o Grey Load Black 230V 230V 230V If loads balanced No Neutral \³/ \³/ \³/ centre = neutral & BLUE ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ loads all get 230V (black) (neutral) The 3 line currents are normaly loaded up to be as equal as possable to reduce the current in the neutral cable normal the same gauge. But Philip M1EUR reports that Neutal cable may need to be 2x the gauge (CSA) if electronic loads with very high harmonic current are used! NEW COLOUR HAZARDS ! New EU colours are Brown Black Grey for Lives & Blue Neutral replacing Red Yellow Blue for Lives & Black Neutral. Green/Yel earth. N.B. the lethal change for both BLACK & BLUE colours! Also note the colour layout of new 3 phase 4 core cable means, that a joint can not be straight to an old cable & bigger joints casings will be needed to allow for at least 2 cores to be bridged! Single phase will change from Red live, Black Neutral to Brown & Blue respectifully. But highly confusing in a 3 phase board with both old black wire loads for Neutrals & Black Bus feed for live! Brown & Blue sleeves are to be used over Red & Black wires! 3 PHASE TRANSFORMERS Like any transformer the voltage can be changed, or isolated etc. The difference being that 3 legs of the transformer carry the windings rather than just the middle. ÚÄÄÄÄÄÄÄÄÄÄÄ¿ The winding connections can be either STAR or ³ ÚÄÄ¿ ÚÄÄ¿ ³ DELTA or combinations of both. ÚÁÄÁ¿ÚÁÄÁ¿ÚÁÄÁ¿ When cross connected star-delta a rotation of Windings->³ 1 ³³ 2 ³³ 3 ³ 90ø in phase occurs. (30ø to other phases) ÀÂÄÂÙÀÂÄÂÙÀÂÄÂÙ . Laminated ³ ÀÄÄÙ ÀÄÄÙ ³ | or / \ becomes _ / or /'³ Core ->ÀÄÄÄÄÄÄÄÄÄÄÄÙ / \ '---' \ '\,³ (due to magneto striction of the core, audio hum given off from the steel is @ 300Hz on 50Hz system) 3 PHASE RECTIFICATION With rectification 3 diodes gives about 30% ripple at 150Hz (3x supply) the ripple is not much as singe phase, as some of the 120ø voltages overlap. ___________________ _³_ _³_ _³_ /|\ /_\ /_\ /_\ | 100% ´ _.-._ _.-._ _.-._ Â Ripple Br ÄÄÄÙ ³ ³ Raw 70%_³ / \ / \ / ³ ³ ³ DC ³ ³ ³ ³ ~ Bk ÄÄÄÄÄÄÄÄÄÙ ³ | ³ ³ ³ ³ ³ ³ ³ | ³³ ³ ³ ³ ³ GyÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ | ÅÄÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄ Phase Angle \|/ 0ø 120 180 240 310 360ø BlÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ 3 PHASE BRIDGE RECTIFIERS Only 6 diodes produce a 3 phase bridge & that gives about 14% @ 300Hz (6x supply) ripple peak to peak, as more of the 60ø voltages overlap. ________________ _³_ _³_ _³_ /|\ /_\ /_\ /_\ | 100% ´ _.-._.-._.-._.-._.-._ Â Ripple Br ÄÄÄ´ ³ ³ | 86% /³ / / \ / \ / \ / \ / ~ ³ ³ ³ | ³ ³ ³ ³ ³ ³ ³ Bk ÄÄÄ)ÄÄÄÄÄ´ ³ Raw ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ DC ³³ ³ ³ ³ ³ ³ ³ Gr ÄÄÄ)ÄÄÄÄÄ)ÄÄÄÄÄ´ | ÅÄÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄ Phase Angle _³_ _³_ _³_ | 0ø 60 120 180 240 310 360ø /_\ /_\ /_\ \|/ ÀÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄ 12 PHASE RECTIFIERS With push pull or 3 phase bridge system, & using both star & delta windings there can effectively be 12 lives that are only 30ø apart. This can also be achieved with push pull phase on each leg of the transforner. | \ / \ | / * + * = * / \ | / | \ Using 2x 3 phase bridges or 12 winding & diodes the resultant ripple is only about 3.6% @ 600Hz, assuming all the voltages are equal! Very little filtering is then needed for say a 100kW Tx HT supply. ________________________ _³_ _³_ _³_ _³_ _³_ _³_ /|\ Floating /_\ /_\ /_\ /_\ /_\ /_\ | . BrDÄÄ´ ³ ³ ³ ³ ³ | 100% ´ _.-.-.-.-.-.-.-.-. = Ripple / \ BkDÄÄ)ÄÄÄ´ ³ ³ ³ ³ | 96% /³ / / /\/\/\/\/\/\/\ '---' GyDÄÄ)ÄÄÄ)ÄÄÄ´ ³ ³ ³ | ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ Windings ³ ³ ³ ³ ³ ³ Raw ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ BrSÄÄ)ÄÄÄ)ÄÄÄ)ÄÄÄ´ ³ ³ DC ³³ ³ ³ ³ ³ ³ ³ ³ ³ ³ ³ | BkSÄÄ)ÄÄÄ)ÄÄÄ)ÄÄÄ)ÄÄÄ´ ³ | ÃÄÄÂÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄÄÄÂÄ Phase Angle / \ GySÄÄ)ÄÄÄ)ÄÄÄ)ÄÄÄ)ÄÄÄ)ÄÄÄ´ | 0ø 30 60 120 180 240 310ø _³_ _³_ _³_ _³_ _³_ _³_ | /_\ /_\ /_\ /_\ /_\ /_\ \|/ ÀÄÄÄÁÄÄÄÁÄÄÄÁÄÄÄÁÄÄÄÁÄÄÄÄ See my Tech bul "AC Theory". Why Don't U send an interesting bul? 73 De John, G8MNY @ GB7CIP
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