SMPS AND POWER

PLANT

MUHAMMADALI MC SDE (KAM) KANNUR

Problems observed in conventional AC

• Harmonics in the system

• Standby is very difficult

• Response to relays are poor

• It is more hazardous

Conventional PowerPlant

• Thyristors (SCR) used in Rectifier Circuit

• Having Very Large size

• Heavy weight

• Low Efficiency

• No scope for modular expansion

• Not able to co-equip with technical room

Steps involved in Powerplant

1. Stepping Down the Input Voltage

2. Rectification

3. Filtering

4. Regulation

Stepping Down the Input Voltage is done by using STAR-DELTA Transformer. High voltage Low Frequency AC is converted into Low Voltage Low Frequency AC.

Rectification

Normally for Rectification is done through,

1. Diode Rectifier

2. Bridge Rectifier

3. SCR Rectifier

4. SCR+Diode Rectifier

Through Diode : Ge type when volt exceeds 0.2 v

Si type when volt exceeds 0.7 v

The circuit is forward biased.

No control over the circuit

Through SCR: 1. Small gate current into the gate of the SCR to be triggered. 2.The gate current to be kept until the current through SCR reaches a point called Leaching Current. 3. Once SCR is turned ON, when the current through SCR reaches a limit called Holding Currrent, SCR will be turned off. 4. SCR have highest rating among Power Electronic Devices. 5. Low Turn ON Power requirement

The rectfication may be,

1. Single Phase Half wave rectifier

2. Single Phase Full wave rectifier

3. Three Phase Half wave rectifier

4. Three Phase full wave rectifier

Filtering: Inductors & Capacitors are used

Inductors will conduct DC &

Capacitors will conduct AC

Regulation: I/P Volt +/- 12% variation

O/P Load 5% to 105% variation

Frequency +/- 4% variation

PowerPlant Components1. Float Rectifier (FR)

2. Battery Charger (BC)

3. Switching Cubicle (SC)

It comes in three types, Single Unit ie, FR, BC, SC together as single Two Unit ie, FR/BC/SC + FR Three Unit ie, FR, BC, SC separate

This can be again categarised as

Single Phase

• 5/ 12 A : Parallelling is not possible

• 25/ 50A : Manual Parallelling possible

Three Phase

• >50 A : Auto Parallelling possible

Float Rectifier Float Voltage per cell is 2.15 v Total Float Voltage is 51.5v

Components of FR

1. Step Down Transformer

2. Rectifier Circuit, Filters

3. Capacitor Bank : 1500 Micro Farad

4. Bleeder Resistance

5. Regulation Circuit

Important terms related with FR

1. Drooping: If the rated current > 105%, then

o/p volt suddenly reduced to 47 v

2. Psphometric Noise: <2mv if Bty connected

<4mv if Bty disconnected

3. Insulation Resistance : Min 5 Mega Ohm

4. Temperature : Limit 50 degree for system

Limit 45 degree for SCR

Limit 150 degree of BR

5.Discharge of Battery: When float volt reaches

49.2v or volt/cell 2.05v

6.Prioratisation: If load of priority > 90% rated

capacity, shared by others

Priority FR works on Constant Voltage and other Non Priorities works on Constant Current.

Cards In FR

• Pulse Transformer Card

• Amplifier Card

• Alarm Card

Battery ChargerComponents of BC

1. Step Down Transformer

2. Rectifier Circuit, Filters

3. Ballast Choke : To limit charging current

Output Voltage is 44 to 65 volts

Initial Charging 14% of rated capacity

Normal Charging 10hrs rate

This may be used as FR & Sick Cell charger

Switching Cubicle To connect three –ves of Battery To connect three FR To connect three BC To supervise Alarms To do Auto parallelling

Here only one switch can be disconnected

at a time , it is done by sollenoid control

Switch Mode Power Supply (SMPS)Advantages:-

1. More Efficient

2. Economical

3. Safer

4. Compact in Size

5. Expansion is easier

6. Power Factor is improved

7. Can be co equipped with technical room

Categarisation of SMPSI. Single Stage Conversion:

Ii. Two Stage Conversion:

I/P AC SUPPLY (400V 50Hz)

STEPPED DOWN BY

TRANSFORMER

RECTIFIED IN TO DC, FILTERING &

REGULATION

I/P AC (400V50Hz)

RECTIFIER CKT

HIGH VOLT DC

HIGH FREQ CONVERTOR

STEP DOWN

TR

RECTIFIER CKT

Classification of SMPS1. Low Capacity Powerplant systems

To provide power to small telecome systems in

Rural, Semi Urban areas

Used with small system such as BTS in Urban

Works where building height is not upto std

(Height of SMPS rack is 1500mm)

6.25/ 12.5/ 25 Amp & 3phase 50 Amp

Battery Backup is high (6 to 72 hrs)

DSCA Unit of SMPS DSCA: Distribution, Switching, Control, Alarm

and Monitoring unit

1.Distribution & Switching:

Input Volt : 320 volt to 480 volt

Frequency : 45 Hz to 65 Hz

Autofloat Voltage : 54v (2.25v/cell) for VRLA

: 52.8v (2.2v/cell) for LA Battery

can be adjusted from 48 to 56 volts

Charging Voltage : 55.2 volt (2.30v/cell)

2.Control, Alm&Monitoring: MP based, menu driven

pgm; using RS485 bus

Physical Structure of SMPSRacks : One Main Rack, One Auxillary,

One Extension

Rectifier Module : Max Two nos in Main & Aux

Three nos in each extension

AC & DC Distn module: In each rack

Metering : In each rack

Power System Controller: In main rack

9 Pin AC Socket AC & DC through terminals

Control Signals through 8 pin Tel jack & terminated

On PSC card (50 volts 5600 watts)

System Level Cards of SMPSPSC Cards:

To generate all supervisory alarms

To monitor the status of rectifier modules

To monitor Bty path current & display status

Temco Cards:

Temperature compensation while Bty charging

Temp Gradient -72mv (3mv/cell) per degree celcius

Display & Alarm Cards:

Contains all Visual & audio alarms

System Level Alarms of SMPS1. Mains on Battery Discharge

2. Battery Isolated

3. System Overload

4. Mains out of range

5. FR/ FC Fail

6. Temco Fail

7. Load Voltage Low

8. Load Voltage High

9. FR/ FC on Charge

10. Mains Available

11. FR/ FC on Float

Thank you