1. Power supplement continuity

The power system supplement was designed in way that the electricity power for BSS substation constantly supplied by two different paths, so the system relatively has high reliability.

2. Simplicity of exploitation

The system was designed so that, the consistent parts automatically are able to be regulated In confrontation with different conditions of exploitation.

3. Voltage stability

According to ways which is done, the line voltage remains stable at the range of 1800to 1200V, DC in accelerating  or braking time.

4. Flexibility

According to the expansion metro lines, the system should be acted in such away that be able to coordinate with the expansion of lines .

5. Initial cost

Because of the existence complete network electrification of trains (power supplement by 3 points about 10  KM distances from each other ,like a ring) the initial cost is relatively high.

6. Maintanability

The system was designed according to the high maintainability and high quality equipments and famous. 

Bulk substation (BSS) :

The place of input feeders of the main network in order to supply the power of metro is called bulk substation or (BSS).

The bulk substation is feeding the traction substation and SSS(station supply substation) that exist in station and depot and workshop.

The input electricity to the BSS is 20KV AC, that after switching operation by two systems of 3 spot cable, 20KV power for TSS and workshop is supplied.

In addition, for more reliability, three BSS substation are rung to each other, if one of the BSS substation exits form the circuit, the other substations supply the necessary power for the network.

The BSS equipments includes :

Normal voltage switches, disconnectors, voltage and current transformators.

Traction substation (TSS) :

The trains necessary power is supplied by TSS. In this substations, 20KV AC, which is received from bulk substations changed to 1500 V.DC by transformators and rectifiers then after some protections transferred to the train by over head catenary. 

Presently, according to the studies there are 9 traction substation to supply electric power for shiraz metro line one.

So, there are about 3 TSS in the range of every BSS which is looped to each other independently in order to supply the electric power.

The equipments of the TSS :

Normal voltage switch, power transformators, 12 pulse rectifier,   normal voltage DC,disconnectors, Direct voltage reducer, AC and DC low voltage disconnector, multipurpose digital unit protection, control system, SCADA and charge battery.

Station supply substation (SSS)

In order to supply necessary electric power depots and work shops, illumination and ventilation systems, elevators, telecommunication, all use SSS(station supply substation) .

In every SSS substation, 20KV AC/ 0.04V, by reducer transformators then is distributed for users.

In every passenger station there are two independent power station, that inorder to the most reliability, the capacity of the SSS transformators should be selected in such a way that, if any substations exists from circuit, another one can supplies all electric loads.

The SSS electric power directly is supplied by BSS. In this way, all SSS during the metro line, is divided into three rings so any ring fed by a BSS. It should be mentioned that, all TSS and SSS transformator belong to the dry (cast – Resin).

Equipments of the SSS are as fallows :
Normal voltage panel, 20 KV to 400V reducer transformators, low voltage panel, UPS and capacitor bank.

Voltage level and electrification system of shiraz metro

Now, There are 750 and 1500 levels of direct voltage in traction system, according to the studies and conditions 1500 direct voltage is considered as the best amount for shiraz metro.

Some advantages of 1500 voltage are  such as :

Reduction of the line current, which causes reduction of energy losses.
Reduction in the number of TSS, which let to the reduction of initial investment and stray current.

Long time life and ability to make over head catenry equipments in country.
The 1500 voltage is also used for suburb trains and for the future expansion of metro.

Adjustment to the metro of the other cities.
Shiraz metro transportation by a cartain which consists of 5 wagon with 100 length and 1500 VDC power supply .

Now, in order to convey the electric power from the TSS to interaction motors with in the vegans is used by the ways of third rail and over head catenary.
The over head catenary is used for shiraz metro electrification its advantages is selected for electrification system of Shiraz metro.

 Some advantages of over head catenary :

Metal consumption saving in contrast with the other electrification methods.
High safety of system for passengers and personals long time life of system and possibility of making equipments for overhead catenary network inside our country.