High Speed Fuse Applications Module 5

Transcription

1 High Speed Fuse Applications Module 5

2 Power Semiconductors GTO SSR Semiconductors: High speed electronic switches used to manipulate electrical power Diode Thyristor IGBT Module 5 - page 2 2

3 Application Examples Paper mills & conveyor belts Large factories & mass production Cranes or lifting equipment Industrial pumps Module 5 - page 3

4 Criteria for Fuse Selection Considerations when choosing the right type of fuse for the protection of semiconductors: 3 levels: 1st level: Total Security, Safety Personal Injuries Accidents Catastrophes 2nd level: Damage limitation of components Integral = I 2 t Voltage overload Thermal Conditions 3rd level: Construction optimization Cliquez et modifiez Intensity of Load le current titre Minimize Space Minimize Cost Module 5 - page 4

5 1st level Total Security, Safety Risk to personnel o Insufficient or incorrect fuse protection o Miss-application o Fault exceeds limits of fuse link Accidents o Overload or short circuit o Maintenance of equipment Catastrophes o Fuse link must not be damaged during fault clearing. o Fuse link must protect against catastrophic failure of equipment Cliquez o Fuse link et must modifiez limit cost of repair le titre Module 5 - page 5

6 2nd level Security of the Components Integral o I²t of fuse must be lower than maximum allowable I²t of device to be protected Voltage across the fuse o The voltage across the fuse during fault clearing must be known. This affects the I²t of the fuse link Peak arc voltage of the fuse o Has to be lower than the breakdown voltage of the component to be protected (and the other nearby components). Operating temperature of the fuse o Must not damage the insulation or other plastic materials in the equipment. Module 5 - page 6

7 3rd level Construction Optimization The nature of the current (intensity/form) o Technical and mechanical conditions should be considered with regard to the installation of fuses in rectifiers. Possible fault types o which may occur and their probability must be known, or decision taken if the component has to be protected or break down should be allowed. Fuse lifetime o Cyclic loads, overloads must be known and taken into Cliquez consideration et modifiez le titre Module 5 - page 7

8 Selection Criteria Summary Voltage (U N) : o Must be Higher than highest possible voltage to be broken down by the fuse o Pay attention to DC-requirements I²t: o I²t is the speed of fuse operation. o I²t value must be smaller than the I²t of the device being protected o Note! I²t varies with voltage. The published I²t is at rated voltage, I²t should be de-rated for the voltage across the fuse during fault occurrence. I N : o Pay attention to cooling and installation conditions, Kb and N as well as cyclic loading factor, G Size: o It has to be considered whether to choose a small and cheaper, but warm and slow fuse, or a larger, more expensive but faster fuse. Module 5 - page 8

9 Selection of fuses for the protection of Regenerative DC-drives - Worked Example Module 5 - page 9

10 Basic Configuration of a Regenerative DC-drive F2 F3 U AC F1 + - U DC The task of the fuses: Short circuit protection of the semiconductors The fuses are situated either as F1 and F3 or as F2 fuses Low power drives: fuses in position F1 and F3 High power drives: fuses in position F2 Module 5 - page 10

11 Specifications for a 1500ADC-drives Drives type: regenerative DC-drives Nominal input voltage (line-line), U ac : 690V ac, 50Hz Nominal output current, I DC I : 1500Adc Cyclic load specification: I DC II : 1200A(100%)/15min 1800A(150%)/60s 1246A RMS cont. I DC III : 1104A(100%)/15min 1656A(150%)/120s 1182A RMS cont. I DC IV : 1104A(100%)/15min 2208A(200%)/10s 1122A RMS cont. Ambient temperature in the cabinet: 40 C Forced cooling: the cabinet is ventilated by means of an electrical fan. The fuses are positioned in the airflow. Average air speed 2m/s Cross section area of connection busbars: 57% of IEC value Semiconductor type: phase control thyristor Semiconductor make: ABB Semiconductors p/n 5STP18F1800 Semiconductor maximum I 2 t value: A 2 s, V RRM, maximum repetitive peak reverse voltage: 1800V Module 5 - page 11

12 Selection of rated voltage of the fuse Analyse circuit to find worse case fault = highest voltage across the fuse during operation. Commutation fault in regenerative DC drives. Short circuit with AC voltage superimposed to DC voltage from motor. Rule: rated voltage of the fuse Un 1,8 x U ac. Actual case U ac =690V U n =1250V. What can we learn from this example: the U n of a fuse is not always simply equal to the supply voltage, therefore analyse the fault situation before choosing the U n. Module 5 - page 12

13 Selection of rated current of the fuse Load current and thermal conditions. Facts: High Speed Fuses are fast acting, have high power losses and high working temperature. The current carrying capability is therefore dependant on various thermal conditions: o Ambient temperature 40 C, Kt = o Forced air cooling 2m/s, Kv = 1.1 o Cross section area of busbars, 57% of IEC standard value: Ke = 0.9 The Load current in each leg will be 0.58 x FLC (I DC I 1500A) = 870A Minimum rated current (In) of the fuse based on a continuous load current: o In 0.58 x I DC I / (Kt x Kv x Ke) = 0.58 x 1500Adc / ( 0.91 x 1.1 x 0.9) = 966A o The next higher standard rated current must be selected o In = 1000A Module 5 - page 13

14 Selection of rated current of the fuse Cyclic load. Considerations o most drives are used for industrial processes with variations in the motor load. o Variations in the fuse load current heats up and cool down the fuse o Heavy thermal cycling leads to mechanical stress premature ageing/opening of the fuse. Solution o Reduce ΔT of the fuse by selecting a higher In (fuse rating). Use the G-Factor! I DC II : G = 1,5 Cliquez I DC et III : G modifiez = 1,6 le titre I DC IV : G = 1,8 Module 5 - page 14

15 Selection of rated current of the fuse Cyclic load Fuse ratings based on pure cyclic loading o In 0.58 x I DC II / (Kt x Kv x Ke) x G (1.5) = o 0,58 x 1246A / (0.91 x 1.1 x 0.9) x 1,5 = 1204A o In 0.58 x I DC III / (Kt x Kv x Ke) x G (1.6) = o 0,58 x 1182A / (0.91 x 1.1 x 0.9) x 1,6 = 1218A o In 0.58 x I DC IV / (Kt x Kv x Ke) x G (1.8) = o 0,58 x 1122A / (0.91 x 1.1 x 0.9) x 1,8 = 1300A Module 5 - page 15

16 Selection of the Specific Fuse Based on consideration regarding Voltage, Current, Thermal conditions and Cyclic loading (combination of I DC I and I DC III ) 170M V 1100A 3KN/110 Pre-arc I 2 t: A 2 s Total operating I 2 t at Un: A 2 s Cliquez Data sheet: et modifiez 170K le titre Drawing: 170X0331 pos. 3 Module 5 - page 16

17 Drawing 170X0331 pos.3,dimensions Module 5 - page 17

18 Data Sheet Data sheet 170K6636 Time-Current curve Module 5 - page 18

19 Data Sheet Data sheet 170K6637 o Cut off curve o I 2 t correction o Arc voltage o Power loss correction Module 5 - page 19