Energy Conservation and Audit
(2020502) - Solved Exam Paper 2023
Group (B)
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Q.2 Explain the importance of energy audit
(ऊर्जा अंकेक्षण के महत्व कि व्याख्या करे ।)
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An energy audit is crucial as it provides a systematic approach to energy management. Its importance lies in:
- Identifying Cost Savings: It pinpoints specific areas of energy waste and inefficiency, leading to direct reductions in energy bills.
- Reducing Energy Consumption: It provides a clear roadmap (Energy Conservation Measures or ENCONs) to reduce overall energy (electricity, fuel) usage.
- Establishing a Baseline: It quantifies current energy use, creating a baseline against which future improvements can be measured.
- Environmental Impact: By reducing energy consumption, it directly reduces greenhouse gas emissions and improves an organization's environmental footprint.
- Improving Efficiency & Reliability: It often identifies oversized or inefficient equipment, and recommends upgrades that improve operational reliability and productivity.
OR (अथवा)
State the needs and benefits of star labelling
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Needs of Star Labelling:
- Consumer Information: To provide a simple, recognizable way for consumers to understand the energy efficiency of an appliance at the point of sale.
- Market Transformation: To encourage manufacturers to design and produce more energy-efficient products to compete in the market.
- National Energy Savings: To help the country reduce its overall energy demand by promoting the adoption of efficient products.
Benefits of Star Labelling:
- For Consumers: Allows for an easy comparison of products. Leads to lower electricity bills and long-term cost savings.
- For Manufacturers: Provides a competitive advantage and a clear benchmark for product improvement.
- For the Nation: Reduces peak power demand, lowers reliance on energy imports, and mitigates environmental impact.
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Q.3 Describe the need of energy conservation in induction motor
(प्रेरण मोटर में ऊर्जा संरक्षण की आवश्यकता का वर्णन कीजिए )
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The need for energy conservation in induction motors is immense because:
- High Energy Consumption: Induction motors are the "workhorses" of industry. They account for a very large portion (often 60-70%) of all industrial electricity consumption.
- Inefficient Operation: Many motors run at partial load or are oversized for their application, which is highly inefficient.
- Losses: Motors have inherent losses (stator & rotor I²R, core losses, friction & windage, stray losses). Conservation efforts aim to minimize these.
- Long Operating Hours: Motors often run for thousands of hours per year, so even a small improvement in efficiency leads to significant cumulative energy and cost savings.
Conserving energy in motors reduces operating costs, lowers maintenance, and extends motor life by reducing heat generation.
OR (अथवा)
State the significant features of soft starter
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Significant features of an electronic soft starter include:
- Smooth Acceleration: Gradually ramps up the voltage to the motor, providing a "soft start" without the sudden torque and current spike.
- Reduced Inrush Current: Limits the high starting current (which can be 6-8 times the full load current), reducing voltage sags in the power system.
- Reduced Mechanical Stress: The smooth start reduces mechanical shock on belts, gears, and couplings, leading to lower maintenance and longer equipment life.
- Smooth Stop: Many soft starters also offer a "soft stop" feature, gradually ramping down the voltage, which is useful for applications like pumping to prevent water hammer.
- Adjustable Parameters: Allows users to set the start voltage, ramp-up time, and ramp-down time to match the application's needs.
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Q.4 State and explain any four commercial losses in transmission and distribution system
(पारेषण एवं वितरण प्रणाली में किन्हीं चार व्यावसायिक हानियों का उल्लेख एवं व्याख्या कीजिए)
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Commercial losses (also known as Aggregate Technical & Commercial or AT&C losses) are non-technical losses, primarily due to lack of revenue, not physical energy dissipation.
- Electricity Theft: Unauthorized tapping of lines, bypassing meters, or hooking directly to the distribution network. This is energy consumed but not billed.
- Meter Tampering: Illegally modifying energy meters (e.g., slowing them down, changing readings) so that they record less consumption than what was actually used.
- Billing Errors: Mistakes in the billing process, such as incorrect meter reading, wrong tariff application, or errors in data entry, leading to under-billing.
- Unmetered Supply: Providing electricity to consumers (e.g., street lights, agricultural pumps in some areas) without any meter. The consumption is estimated, often inaccurately, leading to revenue loss.
OR (अथवा)
Explain use of maximum demand controller as energy conservation equipment
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A Maximum Demand Controller (MDC) is an energy conservation device used in industries with a maximum demand tariff.
Its use is as follows:
- Monitoring: The MDC continuously monitors the plant's total power consumption (kVA or kW) in real-time.
- Predicting: Based on the consumption trend within a demand interval (e.g., 30 minutes), it predicts what the final maximum demand will be at the end of the interval.
- Controlling: A "set point" (the desired maximum demand) is programmed into the controller. If the MDC predicts that the demand will exceed this set point, it automatically takes action.
- Load Shedding: The action involves "shedding" (temporarily switching off) non-essential loads in a pre-programmed priority. For example, it might turn off air conditioning or a non-critical pump for a few minutes.
- Restoring: Once the demand is below the set point, it restores the loads.
By "clipping" these demand peaks, the MDC prevents the plant from incurring heavy penalties for exceeding its contract demand, leading to significant cost savings on the electricity bill. This is a cost-control and conservation measure.
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Q.5 Explain different types of cogeneration in details.
(कोजेनरेशन के विभिन्न प्रकारों को विस्तार से व्याख्या करे)
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Cogeneration (or Combined Heat and Power - CHP) systems are primarily classified based on the sequence of energy use:
1. Topping Cycle Systems:
In this system, fuel is first used to generate electricity. The waste heat from this process is then captured and used for a secondary purpose (process heat, steam, hot water). This is the most common type.- Gas Turbine Topping Cycle: A gas turbine burns fuel to drive a generator (making electricity). The hot exhaust gas (waste heat) is passed through a Heat Recovery Steam Generator (HRSG) to create steam or hot water for process use.
- Steam Turbine Topping Cycle: Fuel is burned in a boiler to create high-pressure steam. This steam drives a turbine (making electricity). The exhaust or "back-pressure" steam from the turbine, which is at a lower pressure, is then used for process heating.
- Reciprocating Engine Topping Cycle: An engine (like a diesel or natural gas engine) drives a generator (making electricity). Heat is recovered from the engine's exhaust gases and the engine jacket cooling water.
2. Bottoming Cycle Systems:
In this system, fuel is first used to provide high-temperature thermal heat for a process (e.g., a furnace, kiln). The waste heat from this process, which is still at a high temperature, is then captured and used in a waste heat recovery boiler to generate steam, which in turn drives a turbine to produce electricity. These are less common and are used in high-temperature industrial processes.
OR (अथवा)
State the different types of tariffs. Explain any one
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Different types of tariffs include:
- Flat Rate Tariff: A single, uniform price per unit of energy (kWh) consumed, regardless of total consumption or time of day.
- Block Rate (or Step Rate) Tariff: The price per unit changes in "blocks." For example, the first 100 kWh might be at one price, the next 200 kWh at a lower price, and so on.
- Two-Part Tariff: The bill is split into two components: a fixed charge (based on connected load or max demand, in kW or kVA) and a running charge (based on energy consumed, in kWh).
- Maximum Demand Tariff: Similar to a two-part tariff, but the fixed charge is based on the consumer's maximum demand recorded during the month.
- Time-of-Use (TOU) / Time-of-Day (TOD) Tariff: The price per unit (kWh) varies depending on the time of day the energy is used.
Explanation of Time-of-Use (TOU) Tariff:
This tariff structure is designed to reflect the utility's cost of generating electricity, which varies throughout the day. The day is divided into time periods:- Peak Period: (e.g., 6 PM - 10 PM) When demand is highest. Electricity is most expensive during this time.
- Off-Peak Period: (e.g., 10 PM - 6 AM) When demand is lowest. Electricity is cheapest.
- Shoulder/Standard Period: (All other times) A price in between peak and off-peak.
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Q.6 State any four advantages of energy audit.
(ऊर्जा अंकेक्षण के कोई चार लाभ का उल्लेख करे ।)
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Four main advantages of an energy audit are:
- Reduces Energy Costs: Identifies energy and cost-saving opportunities, leading to a direct reduction in electricity and fuel bills.
- Identifies Energy Waste: Pinpoints specific equipment, processes, or areas where energy is being used inefficiently or wasted.
- Reduces Environmental Impact: By reducing energy consumption, the audit helps reduce the facility's carbon footprint and greenhouse gas emissions.
- Improves Operational Efficiency: Often identifies opportunities to improve processes, optimize equipment operation, and enhance system reliability, which can increase productivity.
OR (अथवा)
Explain in brief Sankey diagram
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A Sankey diagram is a type of flow diagram used to visualize energy balance. In this diagram, the flow of energy is represented by arrows, where the width of the arrow is proportional to the quantity of energy it represents.
The diagram starts with the total energy input (e.g., 100% of electricity input). This main arrow then splits to show how the energy is distributed:
- One branch might show "Useful Energy Output" (e.g., heat in a furnace, light from a lamp).
- Other branches will show "Energy Losses" (e.g., heat loss through walls, motor losses).
Group (C)
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Q.7 Explain the working principle of automatic power factor controller
(स्वचालित पावर फैक्टर नियंत्रक के कार्य सिद्धांत की व्याख्या करे)
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The Automatic Power Factor Controller (APFC) is a device that automatically maintains the power factor of a system close to unity (e.g., 0.99).
Working Principle: It works on the principle of continuously monitoring the reactive power (kVAR) of the load and compensating for it by switching capacitor banks on or off.
Operation Steps:
- Sensing: The APFC panel is connected to the main power line via Current Transformers (CTs) and Potential Transformers (PTs). These sensors feed the real-time voltage and current signals to the controller's relay.
- Calculating: The relay calculates the phase angle between the voltage and current, thus determining the system's instantaneous power factor (PF).
- Comparing: This measured PF is compared to a pre-programmed target PF (e.g., 0.99).
- Switching Action:
- If Measured PF is LOW: (e.g., 0.85, indicating high inductive load), the controller sends a signal to a contactor to switch ON the first capacitor bank. This adds leading kVAR to the system, improving the PF.
- The controller waits, recalculates, and if the PF is still low, it switches on the *next* capacitor bank. This continues step-by-step.
- If Measured PF is HIGH: (e.g., 0.98 capacitive, indicating over-compensation), the controller switches OFF a capacitor bank.
OR (अथवा)
Explain energy efficient motor. Describe its significant features, advantages and limitations.
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An Energy Efficient Motor (EEM) is a motor that is designed to produce the same power output (shaft power) as a standard motor but consumes less input electrical energy. It achieves this by minimizing internal energy losses.
Significant Features: EEMs achieve higher efficiency through design and material improvements:
- Better Materials: Use of higher-grade, thinner steel laminations to reduce core (eddy current) losses.
- More Copper: Increased volume of copper windings in the stator to reduce I²R (resistance) losses.
- Improved Design: Tighter air gap between stator and rotor, better aerodynamic fan design (less windage loss), and precision-balanced rotor.
Advantages:
- Lower Energy Bills: Consumes less electricity (kW) for the same work.
- Longer Life: Runs cooler due to lower heat losses, which extends the life of the winding insulation and bearings.
- Higher Reliability: Better build quality and lower operating temperature lead to fewer failures.
- Lower Noise: Precision engineering and better fans often result in quieter operation.
Limitations:
- Higher Initial Cost: The improved materials and construction make them more expensive to buy than standard motors.
- Payback Period: The cost saving only becomes apparent over time. The payback period must be calculated to justify the investment.
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Q.8 Explain the following energy conservation techniques: i) Controlling I²R losses ii) Balancing phase current
(निम्नलिखित ऊर्जा संरक्षण तकनीकों की व्याख्या करें; ⅰ) I²R हानियों को नियंत्रित करना ii) संतुलन चरण वर्तमान )
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i) Controlling I²R Losses:
I²R losses (or "copper losses") are the heat losses caused by electrical current (I) flowing through the resistance (R) of a conductor (like a cable or motor winding). These losses are proportional to the square of the current.
To control these losses:- Reduce Current (I): The most effective method. This is done by improving the power factor. For the same active power (kW), a higher power factor (closer to 1) means less total current (kVA).
Reduce Resistance (R): Use larger cross-section cables, which have lower resistance. This is especially important for long cable runs. Also, using energy-efficient motors with more copper windings reduces winding resistance.- Use High Voltage Transmission: For the same power, higher voltage means lower current, which drastically reduces I²R losses (this is why power is transmitted at high voltage).
ii) Balancing Phase Current:
In a three-phase system, if the single-phase loads (like lights, computers, small appliances) are not distributed equally across the three phases, the system becomes unbalanced.
This unbalance causes:- A high current to flow in the neutral wire, which is a waste of energy (I²R loss in the neutral).
- Overheating and inefficient operation of three-phase motors.
- Overloading of one phase while others are under-loaded.
OR (अथवा)
Explain energy conservation method in lighting system by using installation of separate transformer servo stabilizer
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This method conserves energy by ensuring the lighting circuit receives a stable, optimal voltage, and is not affected by other loads.
1. Separate Transformer for Lighting:
Industrial loads (like motors, welders) cause frequent voltage fluctuations (sags and swells) in the power system when they start and stop.
By installing a dedicated transformer that feeds *only* the lighting circuits, the lighting load is isolated from these fluctuations. This results in a stable voltage, which prevents lamps (especially HID and fluorescent) from flickering or failing prematurely.2. Servo Stabilizer:
Often, the grid voltage supplied to a facility is higher than the rated voltage (e.g., 240-250V instead of 220-230V). Lighting fixtures operating at this higher voltage consume significantly more power (over-wattage) and have a drastically reduced lifespan.
A Servo Stabilizer (or voltage stabilizer) is installed on the lighting circuit (often after the separate transformer). It continuously monitors the output voltage and uses a servo motor to adjust a transformer tap, ensuring the output voltage is always stable and at the optimal level (e.g., 220V).Combined Benefit: The separate transformer provides isolation, and the servo stabilizer provides optimal, stable voltage. This combination saves energy by eliminating over-wattage consumption and also saves money on maintenance and lamp replacement costs.
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Q.9 With the help of neat diagram explain steam turbine co-generation system.
(स्वच्छ चित्र की सहायता से वाष्प टर्बाइन कोजेनरेशन प्रणाली की व्याख्या करें)
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This is a topping cycle cogeneration system. Fuel is used to generate electricity first, and the waste heat (steam) is then used for industrial processes.
Working:
- Boiler: Fuel (like coal, gas, or biomass) is burned in a boiler to produce high-pressure, high-temperature steam.
- Steam Turbine & Generator: This high-pressure steam is fed into a steam turbine. The steam expands and rotates the turbine blades, which in turn drive a generator to produce electricity.
- Process Heat: Instead of condensing all the steam (as in a pure power plant), the low-pressure exhaust steam leaving the turbine is extracted. This "waste heat" still contains significant thermal energy.
- Application: This low-pressure steam is piped to the industrial plant and used for process heating (e.g., drying, boiling, chemical reactions).
- Condensate Return: After the steam gives up its heat in the process, it condenses into hot water (condensate), which is returned to the boiler to be reused, saving energy and water.
OR (अथवा)
Describe the application of tariff system to reduce the energy bill.
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Understanding and applying knowledge of the tariff system is a key way to reduce energy bills without any new equipment:
- Power Factor Improvement: Many tariffs (like Two-Part) include a penalty for low power factor (e.g., below 0.9). By installing capacitor banks to improve the PF, a consumer can avoid these penalties, directly reducing the bill.
- Peak Demand Control: For Maximum Demand or TOU tariffs, the "demand charge" (based on the highest kW or kVA used in a 30-min interval) is a large part of the bill. By scheduling large loads to not run simultaneously, or by using a Maximum Demand Controller, a consumer can "clip" the peak and significantly lower this fixed charge.
- Load Shifting (Time-of-Use): If on a TOU tariff, a consumer can shift energy-intensive operations (like water pumping, charging, large batch processes) from "Peak" hours (most expensive) to "Off-Peak" hours (cheapest). This reduces the average cost per kWh.
- Optimizing Contract Demand: Regularly reviewing the "Contract Demand" (the demand you agree not to exceed) is important. If it's set too high, you pay for capacity you don't use. If it's too low, you pay heavy penalties. Adjusting it to be just above the normal peak demand optimizes costs.
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Q.10 Explain various types of energy audit instrument and their uses.
(विभिन्न प्रकार के ऊर्जा अंकेक्षण इंस्ट्रूमेंट और उनके उपयोगों की व्याख्या करें)
View Answer +
Various instruments are used in an energy audit to measure different parameters:
- Power Analyzer / Data Logger:
Use: A portable instrument with CTs and voltage probes. It measures and records all major electrical parameters: Voltage (V), Current (A), Power Factor (PF), Active Power (kW), Reactive Power (kVAR), Apparent Power (kVA), Energy (kWh), and Harmonics. It's the most important tool for electrical audits. - Flue Gas Analyzer:
Use: A probe inserted into the exhaust stack of a boiler, furnace, or generator. It measures the percentage of Oxygen (O₂), Carbon Monoxide (CO), Carbon Dioxide (CO₂), and the flue gas temperature. This data is used to calculate the combustion efficiency. - Infrared (IR) Thermometer / Thermal Imager:
Use: Non-contact devices to measure surface temperature. An IR thermometer gives a single-point reading, while a Thermal Imager (camera) creates a visual heat map. Used to find "hot spots" in electrical panels (loose connections), faulty steam traps, and missing insulation on pipes or walls. - Lux Meter:
Use: Measures the illuminance level (in Lux) in an area. Used in lighting audits to check if areas are over-lit or under-lit compared to standards, identifying energy-saving opportunities. - Anemometer:
Use: Measures air velocity (in m/s). Used to measure the flow rate in ducts (HVAC systems) or to check for compressed air leaks.
OR (अथवा)
Describe the scenario of transmission and distribution losses at state level and national level.
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National Level Scenario:
Historically, India has had very high Transmission and Distribution (T&D) losses, often exceeding 25-30%. These are a combination of Technical Losses (I²R losses in lines, transformer losses) and Commercial Losses (theft, billing issues, etc.), often referred to as Aggregate Technical & Commercial (AT&C) losses.
In recent years, through government schemes like UDAY (Ujwal DISCOM Assurance Yojana) and infrastructure upgrades (like high-voltage transmission, smart meters), the national average AT&C loss has reduced significantly, coming down to the 15-20% range. However, this is still high compared to the global benchmark of under 10%.State Level Scenario:
The scenario varies dramatically from state to state.- High-Loss States: Some states, particularly in northern and central India, have historically struggled with very high AT&C losses, sometimes exceeding 30% or even 40%, largely due to high commercial losses (theft) and poor infrastructure.
- Low-Loss States: Other states, particularly in southern and western India, have been more successful in reducing losses through privatization of distribution, better metering, and grid modernization. Their losses are often much closer to (or even below) the national average.
- Power Analyzer / Data Logger:
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Q.11 State the benefits of VFDs. How energy conservation is achieved by using VFDs?
(वीएफडी के लाभ बताएं। VFDs का उपयोग करके ऊर्जा संरक्षण कैसे प्राप्त किया जाता है?)
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Benefits of VFDs (Variable Frequency Drives):
- Precise Speed Control: Allows the motor's speed to be matched exactly to the process requirement.
- Soft Start/Stop: Provides smooth acceleration and deceleration, reducing mechanical stress and electrical inrush current.
- High Power Factor: VFDs typically operate at a high power factor (0.95 or better), reducing reactive power draw.
- Protection: Includes built-in motor protection features (overload, under-voltage, etc.).
How Energy Conservation is Achieved:
VFDs achieve massive energy savings primarily in variable torque load applications, such as fans and pumps.
This is due to the "Affinity Laws", which state:- Flow is proportional to Speed (Q ∝ N)
- Pressure is proportional to the square of Speed (P ∝ N²)
- Power is proportional to the CUBE of Speed (kW ∝ N³)
With a VFD, the damper is left 100% open, and the VFD slows the motor down to 80% speed.
According to the affinity law, the power consumed is (0.8)³ = 0.512, or just 51.2% of the original power. By reducing the speed by 20%, the energy consumption is reduced by nearly 50%.
OR (अथवा)
Explain in brief any two of the following: i) Primary and secondary energy (ii) IE Act 2001 (iii) Energy Audit report format
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i) Primary and Secondary Energy:
- Primary Energy: These are energy sources as they are found in nature, before any conversion or transformation. Examples include: raw coal, crude oil, natural gas, solar radiation, wind, and firewood.
- Secondary Energy: These are energy carriers that are derived or converted from primary energy sources. They are more convenient to use. Examples include: Electricity (from coal or gas), Gasoline/Diesel (from crude oil), and Coke (from coal).
ii) IE Act 2001 (Energy Conservation Act, 2001):
This is the key legislation in India that provides the legal framework for energy conservation measures. Its main features are:- Establishment of BEE: It created the Bureau of Energy Efficiency (BEE) as the central body to implement the act.
- Standards & Labelling (S&L): Empowered BEE to set efficiency standards and mandatory star-rating labels for appliances (like ACs, refrigerators).
- Designated Consumers: Identified large, energy-intensive industries (like steel, cement, power plants) as "Designated Consumers" who are required to conduct mandatory energy audits and reduce their energy consumption.
- Energy Conservation Building Codes (ECBC): Introduced building codes for new commercial buildings to ensure they are designed for energy efficiency.
iii) Energy Audit Report Format:
A typical energy audit report is a structured document that presents the findings. A common format includes:- Executive Summary: A one-page summary for management, highlighting total savings, required investment, and overall payback.
- Introduction: Details of the facility, the audit team, and the scope of the audit.
- Energy Use Analysis: Analysis of past energy bills, calculation of Specific Energy Consumption (SEC), and a Sankey diagram showing energy balance.
- Energy Conservation Measures (ENCONs): The core of the report. This is a detailed list of all identified saving opportunities, categorized by (a) Low-cost/No-cost, (b) Medium-cost, (c) High-cost.
- Cost-Benefit Analysis: For each ENCON, it details the required investment, expected annual savings, and the simple payback period.
- Action Plan: A recommended implementation plan.
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