之前講完Loading Estimation 同 Cable Sizing, 今個Post就講下Genset Sizing. 講埋Genset Sizing, 電既 Major Equipment Sizing 應該講曬. 所以黎緊之後我打算會講下其他野, 暫時諗到既就係Lighting/UPS/AHF/CBS. 當然電仲有好多野可以講, 仲有Lift & Escalator都可以講講.
Introduction
Generator, 姐係發電機, 顧名思義就係可以發電既機器. 個Concept就係利用利用柴油(Diesel Fuel)去推動Generator入面既Engine. 係呢個過程之中, Generator入面既Alternator就會將Motor Power轉做Electrical Power, 從而發電. 想知多啲可以睇下有關 AC Motor 既教科書.
香港黎講, 主要有2類型Genset: FSI (Fire Services Installation) Genset同Non-FSI (Non Fire Services Installation) Genset. FSI Genset就要跟消防局既Requirement, 姐係15秒内要著到同要有足夠油量去維持6個鐘頭既Full Load Operation.
係香港, Generator主要係用黎做Secondary Power Supply. 事關我地平時都係靠市電發電, 姐係中電/港燈由佢地132kV Substation以地筒形式拖10幾條11kV電綫去到我地大廈既牛房到, 再經隻牛將11kV Step down到去380V(三相)/220V(單相), 先再送到去制櫃, 再派比唔同樓層. 但當然, 我地都有機會有情況係無市電到. 呢個情況唔一定係中電/港燈無電, 可能係制櫃要做5年檢/或者制櫃真係唔好彩, 入面爆BAR/BUSDUCT, 咁呢啲情況都會可以令到無市電到. 如果牽涉到一啲 Sensitive Load(例如 Server/Data Center/IT Equipment), 就會著Non-FSI Genset. 同一個Concept, FSI Genset 都係無Normal 電先著, FSD COP都有寫:
5.8d) Failure of one or more phases of the main supply, or a reduction of voltage to less than 70% of normal, for a duration exceeding 1 second, shall initiate automatic starting of the emergency generator set.
Codes of Practice for Minimum Fire Service Installation and Equipment, 2012, HKFSD
Requirements for Generator Sizing
要Size Genset 有以下幾個Criteria 要 fulfill到:
- Genset Rating (kW) > Total Steady Load (kW)
- Genset Rating (kVA) > Total Steady Load (kVA)
- Max. Transient Load in any step (kW) <= Step Load Acceptance of the Genset (kW)
- Genset Overload Capacity (kW) > Max. Transient Load (kW)
- Voltage Dip <= 20%
1. Genset Rating (kW) > Total Steady Load (kW)
通常第一步都係好似計Loading咁, List out曬成個Project既Essential Load, 佢地既Power Factor, Starting Method…等等. Steady Load姐係過左Starting之後行順左既Load. 加曬所有Steady Load之後, 個總數要細過Genset既Rating.
2. Genset Rating (kVA) > Total Steady Load (kVA)
唔同Load會有機會有唔同Power Factor, 所以可能Power Factor細個啲會出到大啲既kVA, 所以所有Essential Load既總kVA都要細過Genset 既 kVA Rating. Genset就要睇Catalogue, 通常Power Factor係0.8.
Genset Rating in KVA = Genset Rating in kW / Power Factor.
同樣地, 加曬所有Steady Load (kVA)之後, 個總數要細過Genset既Rating (kVA).
3. Maximum Transient Load in any Step (kW) <= Step Load Acceptance of the Genset (kW)
呢個時候就要開始幫Genset分Step (Step 1, Step 2, Step 3…), 因爲每部Genset都有一個Step Load Acceptance (通常計數用60%, 因爲睇過Cummins 啲Catalogue最細係60%, 煥然之Step Load Acceptance就會係 Genset Rating in kW x 60%), 呢個數係代表Genset每個Step最多可以Start到幾大既Loading. 所以好難一次過Group曬一個Step咁起.
Transient Load 其實就係解 Starting Current, 所以簡單啲就係Genset最大個個Step既Transient Load要細過Genset既Step Load Acceptance. Operation上, 其實就係每個Step順次序咁行. 所以如果FSI Genset, 就可能要諗下有D咩係起Genset既時候第一時間要著, 有啲咩係遲啲著都無所謂..
切記如果Essential Load有好多摩打相關既Load (例如Pump, Chiller) 就最好問好曬相關同同事啲Pump/Chiller既Motor Rating. 因爲ArchSD EE GS裏面規定唔同kW既Motor要用咩Starting Method (詳情睇翻ArchSD EE GS 2017 C5.26.4). 如果用DOL Start, Starting Current Multiplier會係6倍, S/D就2.5倍, VSD就1倍., 呢個好重要, 因爲Starting Method係會直接影響到Genset要分幾多個Step, Starting Current大左自然就要分多左Step. EMSD亦都有個Summary Table:
4. Genset Overload Capacity (kW) > Maximum Transient Load (kW)
頭先都講左Genset起機既時候個Operation, 就係一個一個Step咁起. 每一個Step行順左先會著下一個Step. 所以最後會有個總數係講Max. Transient Load. 呢個數可以理解為:
起好曬既Step既Steady Load + 最後起既Step既Transient Load
呢個係講緊當Genset起最後個Step個陣, 實際孭緊幾多Load. Genset 自己本身會允許一個10%既Overload, 所以Genset 個Overload要頂到Max. Transient Load. 總結:
Genset Rating (kW) x 1.1 > Max. Transient Load (kW)
5. Voltage Dip <= 20%
Genset係起Step既時候, 凍機撻著啲Load會有機會有Voltage Dip. 所以我地要揾翻最大既Step, 然後睇翻Genset既Voltage Dip Curve (唔同Rating唔同機都有唔同Curve, 要問Genset Supplier攞), 示意圖如下 :
對應翻最大個Step既Transient Load (kVA), 篤翻380V條Curve, 個Voltage Dip 要細過20%.
Conclusion
上述既五大訴求就係Size Genset要注意既地方. 至少我自己Size Genset都係跟上面既Criteria去計, 如有補充請留言話我知
當然計Genset只係其中一部分, 我地仲要計油缸同用油量. 遲啲會出多個Post講埋.
最後, 如果你覺得幫到你, 記得Share出去比你既朋友or同學仔!!
Alisa Li
please talk about Lift & Escalator. Thanks!
AC
Sure! Will talk about L&E later.
ALISA LI
Would you also like to put on an example for calculation? Such a building supply 2500A which Essential power need to maintain 2 hours for fireman lift and FS pump etc. Thanks.
AC
I will give an example in the next post because next post is about fuel tank calculation…but first I would like to comment on your question. If the genset is supplying fireman lift & FS pump…etc, that genset should be a FSI-genset. Hence, according to FSD COP, fuel maintaining 6 hours of full load operation of the genset should be provided.
(Y_Y)
資料好有用, 但唔好意思, 想問下d野, 我見房署盤計Genset會考慮埋regenerative power absorption, 想問下其他非房署盤既Job係未唔會考慮?
(Y_Y)
Step 3
Then check against regenerative power absorption capacity taking into account of the basic load being connected to the essential circuit. If regenerative power absorption capacity cannot meet that from the lifts, dummy load is added to absorb excess amount of the regenerative power by the electrical sub-contractor;
AC
係, 你講個個係BEC要求既, 應該係要求2.5m/s and 1000 kg above 既Lift要加Regenerative Braking省電.
Housing份Internal Genset Sizing會check Regenerative Load要細過Genset maximum 頂到既 Regenerative Load (通常Genset會頂到Rating x 10%既Re. Load). Housing要check既主要原因我諗應該係因爲Housing既Emergency Lighting & Power Load太細. 因爲Regenerative Load會送翻電去個Source到, 如果係著Genset既情況底下送翻去個部Genset到有機會會令到Genset個Motor Overspeed, 從而影響到Lighting & Power Load. 而因爲Housing既Emergency Lighting & Power Load太細, Lift既Regenerative Power係會大過L&P Load, 所以係會有正Regenerative Power (Lift Regen Power – L&P Load). 但其他non-residential project普遍都有一定既L&P Essential Load, 所以Lift既Regen唔會做到正Regen Power, 所以係負Regen Power既情況下, 就唔會有電翻Genset, 所以唔需要再Check.
(Y_Y)
Thank, 睇過咁多香港工程blog, 覺得師兄做得最好最詳細
發電機佬
如果有了 Genset 的 Step Load Acceptance (in kW)，又有了各個 FS pump, Staircase Pressurization Fan 等等的 starting kVA，請問怎樣去評估 genset 是否應付到呢？
AC
其實入曬所有Load, 做到以下幾點就得:
1. Genset Rating > Total Steady Load
2. Max. Transient Load per Step <= Step Load Acceptance 3. Genset Overload Capacity > Max. Transient Load
4. Voltage Dip <= 20%
FK
For FSI genset, if all loads are FSI loads, does it mean that all loads shall be started already in the first step? i.e. all fsi max traisient loads <=step load acceptance. there will be no step 2,3,etc… generator capacity will be wasted as the remaining capacity will not be used in the other steps.