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Table 1: Advantages and disadvantages of alternative UPS systems
Rotary diesel ups Hybrid rotary ups Static ups
Range of units 1 MVA to 2 MVA 150 kVA to 800 kVA 3 kVA to 800 kVA
Advantages Pure sinusoidal wave output voltage Pure sinusoidal wave output voltage Inexpensive installation costs
Less than 2% distortion Less than 2% distortion Inexpensive supply conditioning to critical load
No major battery maintenance Marginally cheaper alternative to rotary system Ability to split ups and generator components to optimise plant layout, builders work and adjacencies with loads
Single system offering back-up protection to critical and essential loads Better reliability than static system  
Superior handling of load faults Better handling of high load faults than static system  
Better performance than static systems when handling fluctuating loads Better performance than static system when handling fluctuating loads  
Lower space requirement than for separate generator and ups installations Ability to split ups and generator components to optimise plant layout, builders work and adjacencies with loads  
Cheaper and simpler maintenance than for separate generator and ups installations    
Protection against prolonged power outages    
Improves power factor    
Reduced cooling requirement with no heat build-up from banks of batteries    
Disadvantages Performance reliant on start-up of diesel engines Requirement for battery maintenance Stepped sinusoidal wave-form output
High installation costs Generator required for essential loads Higher levels of distortion than rotary solutions
Potential adjacency of diesel generator to occupied space Critical load protection duration dependent on battery storage limits, typically 10 min only Requirement for battery maintenance
    Generator required for essential loads
    Performance affected by fluctuating loads
    High load faults cleared by switching to bypass mode
    Critical load protection duration dependent on battery storage limits, typically 10 min only
    Distortion generated back-up mains supply to other users
Cost of ups only (£/kVA) n/a £245 – £265 £180 – £200
Cost of ups and standby generation (£/kVA) £450 – £480 £440 – £470 £405 – £435
Indicative space requirement of ups and standby generation (m2/kVA) 0·04 – 0·05 0·06 – 0·07 0·06 – 0·07
Cost Summary
Single generator set installations Total generator duty (kVA)          
250 500 1 000 1 500 2 000  
Generator set 78 100 107 800 150 700 235 400 292 600  
Flue installation (40 m) 11 000 13 200 16 500 24 200 27 500  
24 h local fuel storage & pump assembly 1 700 2 200 3 300 5 500 7 200  
Total cost of installation (£) 90 800 123 200 170 500 265 100 327 300  
Multiple generator sets Total generator duty (kVA)          
750 1500 3 000 4 500 6 000  
Generator set 234 300 323 400 482 100 706 200 877 800  
Synchronising panel 13 200 13 200 13 200 13 200 13 200  
Flue installation (40 m) 33 000 39 600 49 500 72 600 82 500  
24 h local fuel storage & pump assembly 5 000 6 600 9 900 16 500 21 500  
Total Cost of Installation (£) 285,500 382 800 554 700 808 500 995 000  
Static ups installations Total ups 15 min full load capacity (kVA)          
100 250 500 750 1 000 2 000
UPS panel 15 400 23 100 62 700 77 000 154 000 308 000
Batteries 8 800 20 200 28 600 47 300 59 400 118 800
Total cost of installation (£) 24 200 43 300 91 300 124 300 213 400 426 800
Adjustments for 10 min at full load -2 900 -6 700 -9 500 -15 800 -19 800 -39 600
Adjustments for 20 min at full load 2 900 6 700 9 500 15 800 19 800 39 600
Adjustments for 30 min at full load 8 800 20 200 28 600 47 300 59 400 118 800
Cost breakdown
Capital costs (£) Rotary diesel ups Hybrid ups & diesel generator Static ups & diesel generator
4 x 1·7 MVA diesel generators n/a 1 084 000 1 084 000
4 x 1·7 MVA rotary diesel ups 2 253 000 n/a n/a
2 x 3 x 625 kVA hybrid rotary ups n/a 950 000 n/a
2 x 3 x 625 kVA static ups n/a n/a 714 000
Load shedding arrangements 18,000 n/a n/a
Exhaust flues 155 000 155 000 155 000
Fuel storage (7 days) & transfer systems 217 000 217 000 217 000
Cooling 450 000 576 000 576 000
Ventilation 96 000 141 000 141 000
Acoustic treatment to diesel plantroom 35 000 30 000 30 000
3 224 000 3 153 000 2 917 000
£/kVA 474 0 464 429
UPS 253 19  
cost breakdown      
Capital costs (£) Rotary diesel ups Hybrid ups & diesel generator Static ups & diesel generator
4 x 1·7 MVA diesel generators n/a 1 084 000 1 084 000
4 x 1·7 MVA rotary diesel ups 2 253 000 n/a n/a
2 x 3 x 625 kVA hybrid rotary ups n/a 950 000 n/a
2 x 3 x 625 kVA static ups n/a n/a 714 000
Load shedding arrangements 18,000 n/a n/a
Exhaust flues 155 000 155 000 155 000
Fuel storage (7 days) & transfer systems 217 000 217 000 217 000
Cooling 450 000 576 000 576 000
Ventilation 96 000 141 000 141 000
Acoustic treatment to diesel plantroom 35 000 30 000 30 000
3 224 000 3 153 000 2 917 000
£/kVA 474 0 464 429
UPS 253 19  
The following exclusions relate to both tables: inflation beyond first quarter 2001, general builders’ work, allowances for lv switchgear or mains interconnecting busbar/cabling, load shedding other than localised main lv switchgear, main contractors’ overheads, profit and attendance, main contract preliminaries, professional and prescribed fees, contingencies and design reserve, tax allowances, vat. Price levels in the cost model are current at 1st quarter 2001 levels, based on a central London location.