TUGAS ELDA IV

ARIO WICAKSONO DAMANIK
115090052

1. What is a heat sink?

heat sink is a passive heat exchanger component that cools a device by dissipating heat into the surrounding air

2. What are the precautions to  be taken in mounting a device on a heat sink?

The device must be mounted properly on the heat sink to obtain the correct mounting pressure between the mating surface.

3. What is a heat pipe?

A heat pipe or heat pin is a heat-transfer device that combines the principles of both thermal conductivity and phase transition to efficiently manage the transfer of heat between two solid interfaces

4. What are the advantages and disadvantages of heat pipe?

Advantages:

The device may be cooled by heat pipes partially filled with low-vapor-pressure liquid.

Disadvantages:

Heat pipes must be tuned to particular cooling conditions. The choice of pipe material, size and coolant all have an effect on the optimal temperatures in which heat pipes work.

5. What are the advantages and disadvantages of water cooling?

Advantages:

Water is inexpensive and non-toxic. The advantages of using water cooling over air cooling include water’s higher specific heat capacity, density, andthermal conductivity. This allows water to transmit heat over greater distances with much less volumetric flow and reduced temperature difference.

Disadvantages:

Water accelerates corrosion of metal parts and is a favorable medium for biological growth. Dissolved minerals in natural water supplies are concentrated by evaporation to leave deposits called scale. Cooling water often requires addition of chemicals to minimize corrosion and insulating deposits of scale and biofouling.

6. What are the advantages and disadvantages of oil cooling?

Advantages:

• Oil has a higher boiling point than water, so it can be used to cool items at a temperature of 100°C or higher. However, pressurised water-cooling may also exceed 100°C.
• Oil is an electrical insulator, thus it can be used inside of or in direct contact with electrical components.
• Oil is already used as a lubricant, therefore it may serve in a double use arrangement.

Disadvantages:

• Coolant oil may be limited to cooling objects under approximately 200°C – 300°C.
• Parts are hard to take out and put in after the oil is put in.
• Water is almost universally available in case coolant needs to be added to the system, but oil is not.
• Unlike water, oil may be flammable.

7. What is it necessary to determine the instantaneous junction temperature of a device?

The instantaneous junction temperature must always be maintained lower than the acceptable value.

8. What is polarized snubber?

The changing is quick and through the diode when the thyristor is switched on, the  capacitor discharges through R.

 9. What is nonpolarized snubber?

snubber is classed as polarized or non-polarized depending on whether energy moves in or out of the snubber on one edge of the switching waveform

 10. What is the typical value of damping factor for RC snubber?

 The damping factor is proportional to the ratio of the circuit loss and its surge impedance. It determines the trade off between dv/dt and peak voltage. Damping factors between 0.01 and 1.0 are recommended

 11. What is considerations for the design of optimum RC-snubber components?

• Voltage rating of snubber capacitor and snubber resistor

When selecting the capacitor, a number of different voltage ratings has to considered. The main parameters are the rms and the repetitive voltage ratings. The rms voltage the capacitor sees is dependent on the application and on the way it is used. For a 6-pulse bridge, the rms voltage will be a function of the firing angle. It reaches its maximum for firing angles of 0° or 180 °at 0.90 times the sinusoidal rms voltage at the 3-phase input of the bridge. Some capacitor suppliers do not rate their capacitors with an rms current but either with a “rated” AC voltage, which is then defined as either the maximum repetitive peak voltage in operation or as the maximum repetitive peak-to-peak voltage. Peak voltages for this consideration do not include the relatively short transient switching overvoltages discussed above.

•  Power rating of snubber Resistor

When the overvoltage calculation is done as discussed above, the resistance value for the snubber resistor is calculated and it is fairly simple to calculate the energy dissipated in the resistor during thyristor turn-off as well. This information is though not enough to define the appropriate resistor.

 12. What are the characteristics of selenium diodes?

Selenium diodes work much like any other diode. They allow current to flow in a forward direction and block current from flowing in the opposite direction. They have a higher forward bias voltage then silicon and as such generate much more heat then a comparable silicon diode. Most selenium diodes will therefore have an integrated heat sink that helps to dissipate all the heat generated.

 13. What are the advantages and disadvantages of selenium voltages suppressers?

Advantages:

All things being equal, a full wave rectifier will result in a slightly higher DC voltage with less ripple

Disadvantages:

The gradual drop in voltage can destroy a set of outputs before you even know there’s a problem

 14. What are the characteristics of varistor?

• nonlinear current–voltage
• Typical V/I characteristic of a ZnO varistor

The relationship between voltage and current of a varistor can be approximated to: V = C x Iβ

where:

V = voltage

C = varistor voltage at 1 A

I = actual working current

β = tangent of angle curve deviating from the horizontal

 15. What are the advantages and disadvantages of selenium voltages varistor?

Advantages:

Used for protection against transient over voltages

Disadvantages:

Low forward voltage

 16. What is an arcing time of a fuse?

The amount of time that passes from the instant the fuse element or link has melted until the overcurrent is interrupted or cleared.

 17. What is a clearing time of a fuse?

This is the total opening time of a fuse from the occurrence of an overcurrent until the fuse stops current flow. This is the sum of link melting and arcing time.