☀️ Solar Plant HT Evacuation – Detailed Checklist & SOP
High Tension (HT) evacuation is a critical backbone activity in any solar power plant. Proper design, installation, testing, and protection coordination directly impact plant efficiency, safety, grid compliance, and long-term reliability.
⚡ A. HT Evacuation – Design & Planning Checklist
1️⃣ System Design & Grid Approval
✔️ HT voltage level finalized (11 kV / 22 kV / 33 kV) as per DISCOM approval
✔️ Approved Single Line Diagram (SLD) available and stamped by DISCOM
✔️ Short-circuit level study completed and verified
✔️ Protection philosophy finalized (selectivity & coordination ensured)
✔️ Redundancy philosophy (Ring / Radial / Dual source) defined
✔️ Provision for future plant capacity expansion incorporated
2️⃣ Transformer Planning & Placement
✔️ Inverter Duty Transformer (IDT) located close to inverter blocks to minimize LT losses
✔️ Pooling / Main Transformer positioned near load center or switchyard
✔️ HT cable / overhead (OH) line route optimized for minimum length and losses
✔️ Sufficient clearance for maintenance & ventilation ensured
✔️ Proper RCC foundation with oil soak pit / bund wall (if oil-filled transformer)
✔️ Neutral earthing arrangement finalized (resistor/solid earthing as applicable)
3️⃣ HT Cable / Overhead Line Selection
✔️ Conductor size selected based on current carrying capacity, voltage drop & thermal limits
✔️ Insulation class matching system voltage (e.g., 12 kV / 24 kV / 36 kV class)
✔️ Technical loss calculations validated
✔️ Soil resistivity & temperature considered for cable derating
✔️ Proper laying method (direct buried / trench / cable tray / HDPE duct) defined
✔️ Cable route markers & identification plan prepared
4️⃣ HT Switchgear & Protection System
✔️ VCB / RMU rated as per system fault level
✔️ Protection relays configured (OC, EF, UV, OV, REF, Differential if applicable)
✔️ CT/PT ratios correctly selected and verified
✔️ Numerical relay settings approved and documented
✔️ Protection coordination study with DISCOM grid completed
✔️ Mechanical & electrical interlocking logic tested
5️⃣ Earthing & Lightning Protection
✔️ Substation earth resistance within permissible limits (typically <1 ohm)
✔️ Separate earth pits for equipment body, neutral, and lightning arresters
✔️ Transformer, structure, panel earthing continuity verified
✔️ LA installed at line entry & transformer HT/LT side
✔️ Earth grid interconnected and bonded properly
⚡ B. SOP – HT Evacuation Execution
🔹 Step 1: Pre-Execution Preparation
✔️ Approved drawings (SLD, layout, earthing, protection) available at site
✔️ Material inspection & test certificates verified
✔️ Calibration certificates of torque wrench & testing equipment available
✔️ HT safety tools (insulated gloves, discharge rods, rubber mats) available
✔️ Valid work permit & shutdown approval obtained
🔹 Step 2: Installation
✔️ Transformer installed on leveled foundation with correct alignment
✔️ Anchor bolts tightened and torque values recorded
✔️ HT cable bending radius maintained as per manufacturer guidelines
✔️ Correct phase sequence maintained throughout system
✔️ Terminations (heat shrink / cold shrink) executed by trained personnel
✔️ Proper gland earthing & double earthing ensured
🔹 Step 3: Jointing & Terminations
✔️ Approved HT joint kits used
✔️ Conductor surfaces cleaned, oxide removed, and contact grease applied
✔️ Proper crimping tools with correct dies used
✔️ No exposed strands or insulation damage
✔️ Stress control components installed correctly
🔹 Step 4: Testing & Commissioning
✔️ Insulation Resistance (IR) test conducted and recorded
✔️ Hi-Pot / VLF test for HT cables performed
✔️ Transformer ratio, polarity & vector group verified
✔️ Protection relay secondary injection testing completed
✔️ Earth resistance measurement recorded
✔️ Functional checks of breaker trip & close circuits done
🔹 Step 5: Charging & Energization
✔️ Area barricaded and access restricted
✔️ All protection systems in service
✔️ First energization under no-load condition
✔️ Voltage, current & relay indications monitored
✔️ Checked for abnormal sound, vibration, or heating
✔️ Load gradually applied after stability confirmation
⚡ C. Mandatory Safety SOP
✔️ Only authorized and trained personnel permitted
✔️ PPE mandatory: helmet, arc-rated gloves, safety shoes, face shield
✔️ Lock-Out Tag-Out (LOTO) procedure strictly followed
✔️ Live working strictly prohibited
✔️ Danger boards & signage installed at all HT locations
✔️ Emergency response & first aid kit available
⚠️ D. Common Mistakes to Avoid
❌ Oversized HT route increasing losses & cost
❌ Poor termination workmanship leading to partial discharge
❌ Inadequate earthing or improper bonding
❌ Protection mismatch with DISCOM grid settings
❌ Ignoring future expansion provisions
❌ Improper torque or absence of torque marking
🔑 Key Takeaway
HT evacuation is not just about transferring power to the grid — it directly impacts:
✔️ Plant efficiency
✔️ Electrical safety
✔️ Grid compliance
✔️ Operational reliability
✔️ Long-term asset life
A well-designed and properly executed HT system ensures smooth commissioning, minimal downtime, and sustained performance of the solar power plant.
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