Preventive maintenance (PM) in a solar power plant during the night is a best practice, as it allows for the maintenance of high-voltage (HT) equipment, inverters, and switchgear without affecting power generation. This is often referred to as "Non-Solar Hour" maintenance.

 Preventive maintenance (PM) in a solar power plant during the night is a best practice, as it allows for the maintenance of high-voltage (HT) equipment, inverters, and switchgear without affecting power generation. This is often referred to as "Non-Solar Hour" maintenance. 

I. Preventive Maintenance Activities (Night Time)

A. HT Panel (High Tension/Voltage Panel) Maintenance 

Safety & Preparation: Perform Job Safety Analysis (JSA), conduct Tool Box Talk, and ensure proper PPE (rubber gloves, face mask, safety boots, 40 cal/cm² flashover suit).

Isolation: Rack out the breaker from service to test/isolated position and ensure the spring is discharged.

Cleaning & Inspection: Clean the panel with a dry blower, check for dust/moisture, and inspect for signs of arcing, heating, or rodents.

Mechanical Checks: Tighten all electrical connections and busbar joints.

VCB Maintenance: Check VCB rack-in/rack-out alignment, operate VCB to ensure smooth functioning, and check contact resistance.

Relay and Metering: Check the functionality of protective relays and ensure all meters (voltmeter, ammeter) are working.

Lubrication: Apply grease/petroleum jelly on JAW contacts.

Insulation Test: Conduct Megger test to check insulation resistance (IR). 

B. IDT (Inverter Duty Transformer) Maintenance

Visual Check: Inspect for oil leaks, paint condition, and rust.

Tightness Check: Tighten all cable connections and terminals.

Breather & Oil Level: Check the silica gel in the breather (ensure it is blue) and verify the oil level in the conservator tank.

Cleaning: Clean bushings and insulators to prevent tracking.

Temperature Readings: Check WTI (Winding Temperature Indicator) and OTI (Oil Temperature Indicator). 

C. Other Nightly Maintenance Activities

Inverter (PCU) Maintenance: Clean air filters, verify ventilation system functioning, and tighten DC/AC connections.

Array Junction Box (AJB): Check for moisture ingress, tighten terminals, and ensure proper cable management.

Thermography: Perform infrared thermography to identify hot spots in electrical panels. 

II. Illumination Quantity Required As Per Law 

In India, illumination for industrial and outdoor electrical installations is guided by the National Lighting Code (NLC) and electrical safety regulations (CEA Regulations). 

Switchyard & Transformer Area:

General Area Lighting: 20–50 lux is typically required for safe movement.

Task Lighting (Panel working/Maintenance): 100–150 lux is recommended in areas where fine work (tightening, inspecting) is being done.

Control Room/Panel Room: 300 lux is generally required for administrative or inspection tasks.

Emergency Lighting: 10 lux. 

Key Requirements:

Lux Levels: Lux meters should be used, with an accuracy of 5%, to verify levels.

Quality: Light fittings should be designed to minimize glare and avoid sharp shadows.

Compliance: Lighting must comply with the technical requirements to ensure safety during nocturnal maintenance.