Preferred Voltages
The distribution licensee generally prefers to have power at voltages higher than the distribution voltage with the sole aim that the power is received at some grid substation of the licensee and could be distributed/regulated as desired.

Connectivity Concerns
Whereas there is no complexity in the arrangement where the Cogenerator is supplying power directly to a consumer, other arrangements are not simple. The connectivity of power generated from a cogeneration plant with the grid substation of the licensee involves the following issues:

• Mode of operation, synchronous or radial
• Quantum of power to be supplied
• Location of consumption centers
• Power availability in the state
• Cost of the system and interfacing

Impacts
Whether the cogeneration plant has to run in synchronous mode or has to feed some loads radially would be a major factor in deciding the connectivity. If the power to be supplied by the Cogenerator into the grid is of small quantum, the licensee may not be interested in purchasing it. If interested, it has to analyze if such energy is not wasted in incrimental line losses itself. Again, if the energy so supplied is consumed at places far off from the point of supply, it would not be of much value for the licensee.

If the state has surplus power then it may opt for purchasing power from a Cogenerator for selling it outside the state and the connectivity would have to be looked into accordingly.

The cost of laying evacuation lines up to the point of exchange is a major factor in deciding the connectivity with the grid. The effort of the Cogenerator would always be to supply their power to the nearest available point at whatever voltage it may be and without any consideration whether it is the 'out' point of a substation or a tapping point in between. The less invested on the evacuation system, the greater the economic viability and profits.

The practice generally opted for costs of transmission lines and synchronization equipment is that they would be borne by the Cogenerator. However, as the cost of construction of 132 kV and above lines is very high it may be shared by the Cogenerator and Purchaser, but the work will be carried out under the supervision of the Purchaser/Licensee. The minimum capacity may be fixed beyond which such arrangement would be agreed to.

Connectivity
The widely preferred mode of connectivity is as below:
Up to 10 MW - on 33 kV
Above 10 MW - on 132 kV
The power from the Cogenerator is transmitted at 33/132 kV voltage through a 33/132 kV line from the mill. The power so transmitted will be interfaced with the Purchaser's 132 kV or higher voltage grid substation.

In case of evacuation of power to the grid substation through a 33 kV line, the full cost of the 33 kV line would be borne by the Cogenerator. In case of evacuation through a 132 kV or higher line, it becomes difficult for the Cogenerator to bear the cost, and as such the cost of the 132 kV or higher voltage line from the plant to the designated substation of the Purchaser is decided mutually. In Uttar Pradesh, the entire cost of interfacing at both ends (the mill and UPPCL), the Transmission System, including work at the UPPCL substation, cost of bay, tie-line, if any, and replacement/up-gradation of existing equipment, if any, would be borne by the Cogenerator. Whereas the 132 kV line cost is shared equally. The work relating to transmission and interfacing within the mill premises would be done by the Cogenerator.

The construction of the transmission line and other supporting works indicated above, as the case may be for evacuation of power, shall be done by the Purchaser/or Cogenerator as mutually decided. The technical and other work specifications shall be finalized with the Purchaser/Licensee's approval in accordance with standards and specifications. The construction of 132 kV or higher voltage line, for which the cost of line is shared, shall generally be done by the Purchaser/Licensee, or the Cogenerator at the Purchaser's discretion. Such a line constructed for evacuation of power from the plant, shall not be used for transmitting/supplying power for any other purpose, without mutual agreement between the Cogenerator and the Purchaser. Existing transmission/distribution lines of the Licensee/Purchaser may be utilized for evacuation of power from the plant to the Grid Substation on mutual agreement.

Regulatory mechanisms have added a new dimension to this issue as all these arrangements are to be approved.

System Maintenance
The maintenance of equipment at the generating end shall be done by the plant to the satisfaction of the Purchaser. The maintenance of 33/132 kV or higher voltage lines and terminal equipment at the Purchaser substation shall be done by the Purchaser, annual maintenance charges being payable by the Cogenerator.

Any work to be done by the Cogenerator shall only be with specific approval of the Purchaser or Regulatory Commission as the case may be.

Without limiting the foregoing, the Cogenerator and Purchaser shall install, operate and maintain the interconnection and parallel operation facility in accordance with accepted good engineering practices in the electricity industry and Electricity Grid Code.

Protective Equipment & Interlocking
The interconnection facilities shall include necessary protective equipment and interlocking devices, which shall be so coordinated that any malfunctioning or abnormality in the generators or in the bus of the motor controller shall not adversely reflect on or affect the grid system. In the event of any malfunctioning or abnormality, the system shall be designed to ensure that the Cogenerator breaker isolates its system.

Arrangements at the Point of Supply
The Cogenerator shall make all arrangements for paralleling the set/s with grid in consultation with, and to the satisfaction of the Purchaser, subject to various safety codes.

Synchronization
The mill would synchronize its power generating set with the Purchaser's system with all due care and notice to the Purchaser.

The Purchaser would not be responsible for the damage, if any, caused to the plant and equipment of the Cogenerator due to failure of the synchronizing or protective system provided by them.

Metering
The Cogenerator shall provide two identical sets of Time of Day (TOD) frequency sensitive static meters, with the facility for downloading data to measure the quantity and time details of the power exported and imported, conforming to the specifications approved mutually along with all necessary associated equipment. These meters shall be installed at the interconnection point or as mutually agreed. One set of export/import meters shall be termed the "Bill Meter" and the other set the "Check Meter." The complete metering system consisting of meters, current and potential transformers shall conform to the 0.2 accuracy class, individually and collectively, and shall comply with the technical standards accuracy and calibration requirements of the Indian Electricity Rules and the specifications of the Bureau of Indian Standards.

Operation
The operation of the system would be done as per instruction from the Load Control Center, which in case of the State Licensee is the State Load Despatch Center. The Availability Based Traiff regime coming in to field, and with more consciousness of commercial interests on the part of the Cogenerator as well as the Purchaser, sensitivity of parameters has taken a front seat and is to be taken care of in the best possible manner.